From 6fe6a7ffd380d4a28c0086ec74751e9e738c01ed Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ville=20Syrj=C3=A4l=C3=A4?= Date: Mon, 28 Nov 2016 19:37:14 +0200 Subject: [PATCH] drm/i915: Zero out HOWM registers before writing new WM/HOWM register values MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit On VLV/CHV some of the watermark values are split across two registers: low order bits in one, and high order bits in another. So we may not be able to update a single watermark value atomically, and thus we must be careful that we don't temporarily introduce out of bounds values during the reprogramming. To prevent this we can simply zero out all the high order bits initially, then we update the low order bits, and finally we update the high order bits with the final value. Signed-off-by: Ville Syrjälä Link: http://patchwork.freedesktop.org/patch/msgid/1480354637-14209-13-git-send-email-ville.syrjala@linux.intel.com Reviewed-by: Maarten Lankhorst --- drivers/gpu/drm/i915/intel_pm.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c index cb6b26b9134f..25a5c6787ea8 100644 --- a/drivers/gpu/drm/i915/intel_pm.c +++ b/drivers/gpu/drm/i915/intel_pm.c @@ -877,6 +877,17 @@ static void vlv_write_wm_values(struct intel_crtc *crtc, (wm->ddl[pipe].plane[PLANE_SPRITE0] << DDL_SPRITE_SHIFT(0)) | (wm->ddl[pipe].plane[PLANE_PRIMARY] << DDL_PLANE_SHIFT)); + /* + * Zero the (unused) WM1 watermarks, and also clear all the + * high order bits so that there are no out of bounds values + * present in the registers during the reprogramming. + */ + I915_WRITE(DSPHOWM, 0); + I915_WRITE(DSPHOWM1, 0); + I915_WRITE(DSPFW4, 0); + I915_WRITE(DSPFW5, 0); + I915_WRITE(DSPFW6, 0); + I915_WRITE(DSPFW1, FW_WM(wm->sr.plane, SR) | FW_WM(wm->pipe[PIPE_B].plane[PLANE_CURSOR], CURSORB) | @@ -924,12 +935,6 @@ static void vlv_write_wm_values(struct intel_crtc *crtc, FW_WM(wm->pipe[PIPE_A].plane[PLANE_PRIMARY] >> 8, PLANEA_HI)); } - /* zero (unused) WM1 watermarks */ - I915_WRITE(DSPFW4, 0); - I915_WRITE(DSPFW5, 0); - I915_WRITE(DSPFW6, 0); - I915_WRITE(DSPHOWM1, 0); - POSTING_READ(DSPFW1); } -- 2.20.1