| Message ID | 1369656882-25241-10-git-send-email-andriy.shevchenko@linux.intel.com |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Monday 27 May 2013 05:44 PM, Andy Shevchenko wrote: > Accordingly to dma_cookie_status() description locking is not required. > I think we need lock here: From isr handler, we call dma_cookie_complete() which is in spin-locked. This function updates tx->chan->completed_cookie = tx->cookie; In tegra_dma_tx_status(), we check for dma_cookie_status() which access the chan->completed_cookie; and it decides status based on this As the access of chan->completed_cookie are from different context, we need this locking. But did not get why it is documented as locking is not require if shared variable is getting changed/access from different context simultaneously. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, May 29, 2013 at 1:56 PM, Laxman Dewangan <ldewangan@nvidia.com> wrote: > On Monday 27 May 2013 05:44 PM, Andy Shevchenko wrote: >> >> Accordingly to dma_cookie_status() description locking is not required. >> > I think we need lock here: > From isr handler, we call dma_cookie_complete() which is in spin-locked. > This function updates tx->chan->completed_cookie = tx->cookie; > In tegra_dma_tx_status(), we check for dma_cookie_status() which access the > chan->completed_cookie; and it decides status based on this > > As the access of chan->completed_cookie are from different context, we > need this locking. You need to have a consistent data in the cookies. This is guaranteed by memory barrier if I got it correctly.
diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c index 33f59ec..019ccfa 100644 --- a/drivers/dma/tegra20-apb-dma.c +++ b/drivers/dma/tegra20-apb-dma.c @@ -767,13 +767,11 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, unsigned long flags; unsigned int residual; - spin_lock_irqsave(&tdc->lock, flags); - ret = dma_cookie_status(dc, cookie, txstate); - if (ret == DMA_SUCCESS) { - spin_unlock_irqrestore(&tdc->lock, flags); + if (ret == DMA_SUCCESS) return ret; - } + + spin_lock_irqsave(&tdc->lock, flags); /* Check on wait_ack desc status */ list_for_each_entry(dma_desc, &tdc->free_dma_desc, node) {
Accordingly to dma_cookie_status() description locking is not required. Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Stephen Warren <swarren@wwwdotorg.org> Cc: linux-tegra@vger.kernel.org --- drivers/dma/tegra20-apb-dma.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)