drm/i915: Add second slice l3 remapping

Certain HSW SKUs have a second bank of L3. This L3 remapping has a
separate register set, and interrupt from the first "slice". A slice is
simply a term to define some subset of the GPU's l3 cache. This patch
implements both the interrupt handler, and ability to communicate with
userspace about this second slice.

v2:  Remove redundant check about non-existent slice.
Change warning about interrupts of unknown slices to WARN_ON_ONCE
Handle the case where we get 2 slice interrupts concurrently, and switch
the tracking of interrupts to be non-destructive (all Ville)
Don't enable/mask the second slice parity interrupt for ivb/vlv (even
though all docs I can find claim it's rsvd) (Ville + Bryan)
Keep BYT excluded from L3 parity

v3: Fix the slice = ffs to be decremented by one (found by Ville). When
I initially did my testing on the series, I was using 1-based slice
counting, so this code was correct. Not sure why my simpler tests that
I've been running since then didn't pick it up sooner.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8b16d47280f9660fe6af04462def2bddfed7ca17..c6e8df73756670ab25d575aa42d26fe63cfd5e54 100644 (file)
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -917,9 +917,11 @@ struct i915_ums_state {
        int mm_suspended;
 };
 
+#define MAX_L3_SLICES 2
 struct intel_l3_parity {
-       u32 *remap_info;
+       u32 *remap_info[MAX_L3_SLICES];
        struct work_struct error_work;
+       int which_slice;
 };
 
 struct i915_gem_mm {
@@ -1686,6 +1688,7 @@ struct drm_i915_file_private {
 #define HAS_FORCE_WAKE(dev) (INTEL_INFO(dev)->has_force_wake)
 
 #define HAS_L3_GPU_CACHE(dev) (IS_IVYBRIDGE(dev) || IS_HASWELL(dev))
+#define NUM_L3_SLICES(dev) (IS_HSW_GT3(dev) ? 2 : HAS_L3_GPU_CACHE(dev))
 
 #define GT_FREQUENCY_MULTIPLIER 50
 
@@ -1946,7 +1949,7 @@ bool i915_gem_clflush_object(struct drm_i915_gem_object *obj, bool force);
 int __must_check i915_gem_object_finish_gpu(struct drm_i915_gem_object *obj);
 int __must_check i915_gem_init(struct drm_device *dev);
 int __must_check i915_gem_init_hw(struct drm_device *dev);
-void i915_gem_l3_remap(struct drm_device *dev);
+void i915_gem_l3_remap(struct drm_device *dev, int slice);
 void i915_gem_init_swizzling(struct drm_device *dev);
 void i915_gem_cleanup_ringbuffer(struct drm_device *dev);
 int __must_check i915_gpu_idle(struct drm_device *dev);

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d00d24f7a9765773c647f0ae6379e779d8e888a8..21a3d69679eeb418e27c847ad3d078dad3450549 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4222,16 +4222,15 @@ i915_gem_idle(struct drm_device *dev)
        return 0;
 }
 
-void i915_gem_l3_remap(struct drm_device *dev)
+void i915_gem_l3_remap(struct drm_device *dev, int slice)
 {
        drm_i915_private_t *dev_priv = dev->dev_private;
+       u32 reg_base = GEN7_L3LOG_BASE + (slice * 0x200);
+       u32 *remap_info = dev_priv->l3_parity.remap_info[slice];
        u32 misccpctl;
        int i;
 
-       if (!HAS_L3_GPU_CACHE(dev))
-               return;
-
-       if (!dev_priv->l3_parity.remap_info)
+       if (!HAS_L3_GPU_CACHE(dev) || !remap_info)
                return;
 
        misccpctl = I915_READ(GEN7_MISCCPCTL);
@@ -4239,17 +4238,17 @@ void i915_gem_l3_remap(struct drm_device *dev)
        POSTING_READ(GEN7_MISCCPCTL);
 
        for (i = 0; i < GEN7_L3LOG_SIZE; i += 4) {
-               u32 remap = I915_READ(GEN7_L3LOG_BASE + i);
-               if (remap && remap != dev_priv->l3_parity.remap_info[i/4])
+               u32 remap = I915_READ(reg_base + i);
+               if (remap && remap != remap_info[i/4])
                        DRM_DEBUG("0x%x was already programmed to %x\n",
-                                 GEN7_L3LOG_BASE + i, remap);
-               if (remap && !dev_priv->l3_parity.remap_info[i/4])
+                                 reg_base + i, remap);
+               if (remap && !remap_info[i/4])
                        DRM_DEBUG_DRIVER("Clearing remapped register\n");
-               I915_WRITE(GEN7_L3LOG_BASE + i, dev_priv->l3_parity.remap_info[i/4]);
+               I915_WRITE(reg_base + i, remap_info[i/4]);
        }
 
        /* Make sure all the writes land before disabling dop clock gating */
-       POSTING_READ(GEN7_L3LOG_BASE);
+       POSTING_READ(reg_base);
 
        I915_WRITE(GEN7_MISCCPCTL, misccpctl);
 }
@@ -4343,7 +4342,7 @@ int
 i915_gem_init_hw(struct drm_device *dev)
 {
        drm_i915_private_t *dev_priv = dev->dev_private;
-       int ret;
+       int ret, i;
 
        if (INTEL_INFO(dev)->gen < 6 && !intel_enable_gtt())
                return -EIO;
@@ -4362,7 +4361,8 @@ i915_gem_init_hw(struct drm_device *dev)
                I915_WRITE(GEN7_MSG_CTL, temp);
        }
 
-       i915_gem_l3_remap(dev);
+       for (i = 0; i < NUM_L3_SLICES(dev); i++)
+               i915_gem_l3_remap(dev, i);
 
        i915_gem_init_swizzling(dev);
 

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index a610f5abcc416f26f6c849333a727a6b9f132848..60a7bac4fc3b1d4eaafe9dff9e457362497bf1e5 100644 (file)
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -888,9 +888,10 @@ static void ivybridge_parity_work(struct work_struct *work)
        drm_i915_private_t *dev_priv = container_of(work, drm_i915_private_t,
                                                    l3_parity.error_work);
        u32 error_status, row, bank, subbank;
-       char *parity_event[5];
+       char *parity_event[6];
        uint32_t misccpctl;
        unsigned long flags;
+       uint8_t slice = 0;
 
        /* We must turn off DOP level clock gating to access the L3 registers.
         * In order to prevent a get/put style interface, acquire struct mutex
@@ -898,45 +899,64 @@ static void ivybridge_parity_work(struct work_struct *work)
         */
        mutex_lock(&dev_priv->dev->struct_mutex);
 
+       /* If we've screwed up tracking, just let the interrupt fire again */
+       if (WARN_ON(!dev_priv->l3_parity.which_slice))
+               goto out;
+
        misccpctl = I915_READ(GEN7_MISCCPCTL);
        I915_WRITE(GEN7_MISCCPCTL, misccpctl & ~GEN7_DOP_CLOCK_GATE_ENABLE);
        POSTING_READ(GEN7_MISCCPCTL);
 
-       error_status = I915_READ(GEN7_L3CDERRST1);
-       row = GEN7_PARITY_ERROR_ROW(error_status);
-       bank = GEN7_PARITY_ERROR_BANK(error_status);
-       subbank = GEN7_PARITY_ERROR_SUBBANK(error_status);
+       while ((slice = ffs(dev_priv->l3_parity.which_slice)) != 0) {
+               u32 reg;
 
-       I915_WRITE(GEN7_L3CDERRST1, GEN7_PARITY_ERROR_VALID |
-                                   GEN7_L3CDERRST1_ENABLE);
-       POSTING_READ(GEN7_L3CDERRST1);
+               slice--;
+               if (WARN_ON_ONCE(slice >= NUM_L3_SLICES(dev_priv->dev)))
+                       break;
 
-       I915_WRITE(GEN7_MISCCPCTL, misccpctl);
+               dev_priv->l3_parity.which_slice &= ~(1<<slice);
 
-       spin_lock_irqsave(&dev_priv->irq_lock, flags);
-       ilk_enable_gt_irq(dev_priv, GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
-       spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+               reg = GEN7_L3CDERRST1 + (slice * 0x200);
 
-       mutex_unlock(&dev_priv->dev->struct_mutex);
+               error_status = I915_READ(reg);
+               row = GEN7_PARITY_ERROR_ROW(error_status);
+               bank = GEN7_PARITY_ERROR_BANK(error_status);
+               subbank = GEN7_PARITY_ERROR_SUBBANK(error_status);
+
+               I915_WRITE(reg, GEN7_PARITY_ERROR_VALID | GEN7_L3CDERRST1_ENABLE);
+               POSTING_READ(reg);
+
+               parity_event[0] = I915_L3_PARITY_UEVENT "=1";
+               parity_event[1] = kasprintf(GFP_KERNEL, "ROW=%d", row);
+               parity_event[2] = kasprintf(GFP_KERNEL, "BANK=%d", bank);
+               parity_event[3] = kasprintf(GFP_KERNEL, "SUBBANK=%d", subbank);
+               parity_event[4] = kasprintf(GFP_KERNEL, "SLICE=%d", slice);
+               parity_event[5] = NULL;
+
+               kobject_uevent_env(&dev_priv->dev->primary->kdev.kobj,
+                                  KOBJ_CHANGE, parity_event);
 
-       parity_event[0] = I915_L3_PARITY_UEVENT "=1";
-       parity_event[1] = kasprintf(GFP_KERNEL, "ROW=%d", row);
-       parity_event[2] = kasprintf(GFP_KERNEL, "BANK=%d", bank);
-       parity_event[3] = kasprintf(GFP_KERNEL, "SUBBANK=%d", subbank);
-       parity_event[4] = NULL;
+               DRM_DEBUG("Parity error: Slice = %d, Row = %d, Bank = %d, Sub bank = %d.\n",
+                         slice, row, bank, subbank);
 
-       kobject_uevent_env(&dev_priv->dev->primary->kdev.kobj,
-                          KOBJ_CHANGE, parity_event);
+               kfree(parity_event[4]);
+               kfree(parity_event[3]);
+               kfree(parity_event[2]);
+               kfree(parity_event[1]);
+       }
 
-       DRM_DEBUG("Parity error: Row = %d, Bank = %d, Sub bank = %d.\n",
-                 row, bank, subbank);
+       I915_WRITE(GEN7_MISCCPCTL, misccpctl);
 
-       kfree(parity_event[3]);
-       kfree(parity_event[2]);
-       kfree(parity_event[1]);
+out:
+       WARN_ON(dev_priv->l3_parity.which_slice);
+       spin_lock_irqsave(&dev_priv->irq_lock, flags);
+       ilk_enable_gt_irq(dev_priv, GT_PARITY_ERROR(dev_priv->dev));
+       spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+
+       mutex_unlock(&dev_priv->dev->struct_mutex);
 }
 
-static void ivybridge_parity_error_irq_handler(struct drm_device *dev)
+static void ivybridge_parity_error_irq_handler(struct drm_device *dev, u32 iir)
 {
        drm_i915_private_t *dev_priv = (drm_i915_private_t *) dev->dev_private;
 
@@ -944,9 +964,16 @@ static void ivybridge_parity_error_irq_handler(struct drm_device *dev)
                return;
 
        spin_lock(&dev_priv->irq_lock);
-       ilk_disable_gt_irq(dev_priv, GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
+       ilk_disable_gt_irq(dev_priv, GT_PARITY_ERROR(dev));
        spin_unlock(&dev_priv->irq_lock);
 
+       iir &= GT_PARITY_ERROR(dev);
+       if (iir & GT_RENDER_L3_PARITY_ERROR_INTERRUPT_S1)
+               dev_priv->l3_parity.which_slice |= 1 << 1;
+
+       if (iir & GT_RENDER_L3_PARITY_ERROR_INTERRUPT)
+               dev_priv->l3_parity.which_slice |= 1 << 0;
+
        queue_work(dev_priv->wq, &dev_priv->l3_parity.error_work);
 }
 
@@ -981,8 +1008,8 @@ static void snb_gt_irq_handler(struct drm_device *dev,
                i915_handle_error(dev, false);
        }
 
-       if (gt_iir & GT_RENDER_L3_PARITY_ERROR_INTERRUPT)
-               ivybridge_parity_error_irq_handler(dev);
+       if (gt_iir & GT_PARITY_ERROR(dev))
+               ivybridge_parity_error_irq_handler(dev, gt_iir);
 }
 
 #define HPD_STORM_DETECT_PERIOD 1000
@@ -2221,8 +2248,8 @@ static void gen5_gt_irq_postinstall(struct drm_device *dev)
        dev_priv->gt_irq_mask = ~0;
        if (HAS_L3_GPU_CACHE(dev)) {
                /* L3 parity interrupt is always unmasked. */
-               dev_priv->gt_irq_mask = ~GT_RENDER_L3_PARITY_ERROR_INTERRUPT;
-               gt_irqs |= GT_RENDER_L3_PARITY_ERROR_INTERRUPT;
+               dev_priv->gt_irq_mask = ~GT_PARITY_ERROR(dev);
+               gt_irqs |= GT_PARITY_ERROR(dev);
        }
 
        gt_irqs |= GT_RENDER_USER_INTERRUPT;

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index af6f93ca72960377888ee4983448857f9281bf3b..c4f9bef6d073e710e62ba54a1f7e197356aaa145 100644 (file)
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -927,6 +927,7 @@
 #define GT_BLT_USER_INTERRUPT                  (1 << 22)
 #define GT_BSD_CS_ERROR_INTERRUPT              (1 << 15)
 #define GT_BSD_USER_INTERRUPT                  (1 << 12)
+#define GT_RENDER_L3_PARITY_ERROR_INTERRUPT_S1 (1 << 11) /* hsw+; rsvd on snb, ivb, vlv */
 #define GT_RENDER_L3_PARITY_ERROR_INTERRUPT    (1 <<  5) /* !snb */
 #define GT_RENDER_PIPECTL_NOTIFY_INTERRUPT     (1 <<  4)
 #define GT_RENDER_CS_MASTER_ERROR_INTERRUPT    (1 <<  3)
@@ -937,6 +938,10 @@
 #define PM_VEBOX_CS_ERROR_INTERRUPT            (1 << 12) /* hsw+ */
 #define PM_VEBOX_USER_INTERRUPT                        (1 << 10) /* hsw+ */
 
+#define GT_PARITY_ERROR(dev) \
+       (GT_RENDER_L3_PARITY_ERROR_INTERRUPT | \
+        IS_HASWELL(dev) ? GT_RENDER_L3_PARITY_ERROR_INTERRUPT_S1 : 0)
+
 /* These are all the "old" interrupts */
 #define ILK_BSD_USER_INTERRUPT                         (1<<5)
 #define I915_PIPE_CONTROL_NOTIFY_INTERRUPT             (1<<18)
@@ -4747,6 +4752,7 @@
 
 /* IVYBRIDGE DPF */
 #define GEN7_L3CDERRST1                        0xB008 /* L3CD Error Status 1 */
+#define HSW_L3CDERRST11                        0xB208 /* L3CD Error Status register 1 slice 1 */
 #define   GEN7_L3CDERRST1_ROW_MASK     (0x7ff<<14)
 #define   GEN7_PARITY_ERROR_VALID      (1<<13)
 #define   GEN7_L3CDERRST1_BANK_MASK    (3<<11)
@@ -4760,6 +4766,7 @@
 #define   GEN7_L3CDERRST1_ENABLE       (1<<7)
 
 #define GEN7_L3LOG_BASE                        0xB070
+#define HSW_L3LOG_BASE_SLICE1          0xB270
 #define GEN7_L3LOG_SIZE                        0x80
 
 #define GEN7_HALF_SLICE_CHICKEN1       0xe100 /* IVB GT1 + VLV */

diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
index 71f6de24444e8f5b2da18968c1ce3ded10b28c4f..3a8bf0c9b5ce8ea1e56cb62623dbdc8c5dfe5cd9 100644 (file)
--- a/drivers/gpu/drm/i915/i915_sysfs.c
+++ b/drivers/gpu/drm/i915/i915_sysfs.c
@@ -119,6 +119,7 @@ i915_l3_read(struct file *filp, struct kobject *kobj,
        struct drm_device *drm_dev = dminor->dev;
        struct drm_i915_private *dev_priv = drm_dev->dev_private;
        uint32_t misccpctl;
+       int slice = (int)(uintptr_t)attr->private;
        int i, ret;
 
        count = round_down(count, 4);
@@ -134,9 +135,9 @@ i915_l3_read(struct file *filp, struct kobject *kobj,
                return ret;
 
        if (IS_HASWELL(drm_dev)) {
-               if (dev_priv->l3_parity.remap_info)
+               if (dev_priv->l3_parity.remap_info[slice])
                        memcpy(buf,
-                              dev_priv->l3_parity.remap_info + (offset/4),
+                              dev_priv->l3_parity.remap_info[slice] + (offset/4),
                               count);
                else
                        memset(buf, 0, count);
@@ -168,6 +169,7 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
        struct drm_device *drm_dev = dminor->dev;
        struct drm_i915_private *dev_priv = drm_dev->dev_private;
        u32 *temp = NULL; /* Just here to make handling failures easy */
+       int slice = (int)(uintptr_t)attr->private;
        int ret;
 
        ret = l3_access_valid(drm_dev, offset);
@@ -178,7 +180,7 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
        if (ret)
                return ret;
 
-       if (!dev_priv->l3_parity.remap_info) {
+       if (!dev_priv->l3_parity.remap_info[slice]) {
                temp = kzalloc(GEN7_L3LOG_SIZE, GFP_KERNEL);
                if (!temp) {
                        mutex_unlock(&drm_dev->struct_mutex);
@@ -198,11 +200,11 @@ i915_l3_write(struct file *filp, struct kobject *kobj,
         * at this point it is left as a TODO.
        */
        if (temp)
-               dev_priv->l3_parity.remap_info = temp;
+               dev_priv->l3_parity.remap_info[slice] = temp;
 
-       memcpy(dev_priv->l3_parity.remap_info + (offset/4), buf, count);
+       memcpy(dev_priv->l3_parity.remap_info[slice] + (offset/4), buf, count);
 
-       i915_gem_l3_remap(drm_dev);
+       i915_gem_l3_remap(drm_dev, slice);
 
        mutex_unlock(&drm_dev->struct_mutex);
 
@@ -214,7 +216,17 @@ static struct bin_attribute dpf_attrs = {
        .size = GEN7_L3LOG_SIZE,
        .read = i915_l3_read,
        .write = i915_l3_write,
-       .mmap = NULL
+       .mmap = NULL,
+       .private = (void *)0
+};
+
+static struct bin_attribute dpf_attrs_1 = {
+       .attr = {.name = "l3_parity_slice_1", .mode = (S_IRUSR | S_IWUSR)},
+       .size = GEN7_L3LOG_SIZE,
+       .read = i915_l3_read,
+       .write = i915_l3_write,
+       .mmap = NULL,
+       .private = (void *)1
 };
 
 static ssize_t gt_cur_freq_mhz_show(struct device *kdev,
@@ -525,6 +537,13 @@ void i915_setup_sysfs(struct drm_device *dev)
                ret = device_create_bin_file(&dev->primary->kdev, &dpf_attrs);
                if (ret)
                        DRM_ERROR("l3 parity sysfs setup failed\n");
+
+               if (NUM_L3_SLICES(dev) > 1) {
+                       ret = device_create_bin_file(&dev->primary->kdev,
+                                                    &dpf_attrs_1);
+                       if (ret)
+                               DRM_ERROR("l3 parity slice 1 setup failed\n");
+               }
        }
 
        ret = 0;
@@ -548,6 +567,7 @@ void i915_teardown_sysfs(struct drm_device *dev)
                sysfs_remove_files(&dev->primary->kdev.kobj, vlv_attrs);
        else
                sysfs_remove_files(&dev->primary->kdev.kobj, gen6_attrs);
+       device_remove_bin_file(&dev->primary->kdev,  &dpf_attrs_1);
        device_remove_bin_file(&dev->primary->kdev,  &dpf_attrs);
 #ifdef CONFIG_PM
        sysfs_unmerge_group(&dev->primary->kdev.kobj, &rc6_attr_group);

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 686e5b23481def673fcf6d3c650cf18ceedc4b75..958b7d8fea8babcf2ea2d0209ae133f0992bddf0 100644 (file)
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -570,7 +570,7 @@ static int init_render_ring(struct intel_ring_buffer *ring)
                I915_WRITE(INSTPM, _MASKED_BIT_ENABLE(INSTPM_FORCE_ORDERING));
 
        if (HAS_L3_GPU_CACHE(dev))
-               I915_WRITE_IMR(ring, ~GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
+               I915_WRITE_IMR(ring, ~GT_PARITY_ERROR(dev));
 
        return ret;
 }
@@ -1000,7 +1000,7 @@ gen6_ring_get_irq(struct intel_ring_buffer *ring)
                if (HAS_L3_GPU_CACHE(dev) && ring->id == RCS)
                        I915_WRITE_IMR(ring,
                                       ~(ring->irq_enable_mask |
-                                        GT_RENDER_L3_PARITY_ERROR_INTERRUPT));
+                                        GT_PARITY_ERROR(dev)));
                else
                        I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
                ilk_enable_gt_irq(dev_priv, ring->irq_enable_mask);
@@ -1020,8 +1020,7 @@ gen6_ring_put_irq(struct intel_ring_buffer *ring)
        spin_lock_irqsave(&dev_priv->irq_lock, flags);
        if (--ring->irq_refcount == 0) {
                if (HAS_L3_GPU_CACHE(dev) && ring->id == RCS)
-                       I915_WRITE_IMR(ring,
-                                      ~GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
+                       I915_WRITE_IMR(ring, ~GT_PARITY_ERROR(dev));
                else
                        I915_WRITE_IMR(ring, ~0);
                ilk_disable_gt_irq(dev_priv, ring->irq_enable_mask);

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 55bb5729bd78a534da094f07fe74714e162a2c9c..3a4e97bd860771b6ad8e3b5d026a35200fcad4d3 100644 (file)
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -38,10 +38,10 @@
  *
  * I915_L3_PARITY_UEVENT - Generated when the driver receives a parity mismatch
  *     event from the gpu l3 cache. Additional information supplied is ROW,
- *     BANK, SUBBANK of the affected cacheline. Userspace should keep track of
- *     these events and if a specific cache-line seems to have a persistent
- *     error remap it with the l3 remapping tool supplied in intel-gpu-tools.
- *     The value supplied with the event is always 1.
+ *     BANK, SUBBANK, SLICE of the affected cacheline. Userspace should keep
+ *     track of these events and if a specific cache-line seems to have a
+ *     persistent error remap it with the l3 remapping tool supplied in
+ *     intel-gpu-tools.  The value supplied with the event is always 1.
  *
  * I915_ERROR_UEVENT - Generated upon error detection, currently only via
  *     hangcheck. The error detection event is a good indicator of when things