From 7b09a1bba4091a9d208481d7831682a1f3061ab9 Mon Sep 17 00:00:00 2001 From: Robert Jarzmik Date: Wed, 30 Sep 2015 19:42:15 +0200 Subject: [PATCH] dmaengine: pxa_dma: fix residue corner case A very tiny temporal window exists in the residue calculation where : - upon entering residue calculation, the transfer is ongoing - when reading the current transfer pointer, it just changed to the "finisher/linker" descriptor In this case, the residue returned is the whole transfer length instead of 0. Fix it. This appears almost in one extreme case, where the driver is used by older clients which inquire for residue in interrupt context, such as the smsc91x ethernet driver, in a tight loop : interrupt_handler() dmaengine_submit() do { dmaengine_tx_status() } while (residue > 0 || status != DMA_ERROR) Signed-off-by: Robert Jarzmik Signed-off-by: Vinod Koul --- drivers/dma/pxa_dma.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c index 064a8266a3b7..fc4156afa070 100644 --- a/drivers/dma/pxa_dma.c +++ b/drivers/dma/pxa_dma.c @@ -1186,6 +1186,16 @@ static unsigned int pxad_residue(struct pxad_chan *chan, else curr = phy_readl_relaxed(chan->phy, DTADR); + /* + * curr has to be actually read before checking descriptor + * completion, so that a curr inside a status updater + * descriptor implies the following test returns true, and + * preventing reordering of curr load and the test. + */ + rmb(); + if (is_desc_completed(vd)) + goto out; + for (i = 0; i < sw_desc->nb_desc - 1; i++) { hw_desc = sw_desc->hw_desc[i]; if (sw_desc->hw_desc[0]->dcmd & PXA_DCMD_INCSRCADDR) -- 2.20.1