Commit 7b09a1bb authored by Robert Jarzmik's avatar Robert Jarzmik Committed by Vinod Koul

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: default avatarRobert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: default avatarVinod Koul <vinod.koul@intel.com>
parent e87ffbdf
...@@ -1186,6 +1186,16 @@ static unsigned int pxad_residue(struct pxad_chan *chan, ...@@ -1186,6 +1186,16 @@ static unsigned int pxad_residue(struct pxad_chan *chan,
else else
curr = phy_readl_relaxed(chan->phy, DTADR); 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++) { for (i = 0; i < sw_desc->nb_desc - 1; i++) {
hw_desc = sw_desc->hw_desc[i]; hw_desc = sw_desc->hw_desc[i];
if (sw_desc->hw_desc[0]->dcmd & PXA_DCMD_INCSRCADDR) if (sw_desc->hw_desc[0]->dcmd & PXA_DCMD_INCSRCADDR)
......
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