linux-kernel - Re: [PATCH 7/8] dmaengine: tegra20-apb-dma: Only calculate residue if txstate exists.

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Date:	Wed, 8 Jun 2016 09:51:57 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Peter Griffin <peter.griffin@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <kernel@...inux.com>,
	<vinod.koul@...el.com>, <linus.walleij@...aro.org>,
	<dan.j.williams@...el.com>, <leoli@...escale.com>,
	<zw@...kernel.org>, <baohua@...nel.org>,
	<maxime.ripard@...e-electrons.com>, <wens@...e.org>,
	<ldewangan@...dia.com>, <swarren@...dotorg.org>,
	<thierry.reding@...il.com>, <gnurou@...il.com>
CC:	<lee.jones@...aro.org>, <dmaengine@...r.kernel.org>,
	<linux-tegra@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 7/8] dmaengine: tegra20-apb-dma: Only calculate residue if
 txstate exists.

Hi Peter,

On 07/06/16 18:38, Peter Griffin wrote:
> There is no point calculating the residue if there is
> no txstate to store the value.
> 
> Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> ---
>  drivers/dma/tegra20-apb-dma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
> index 01e316f..7f4af8c 100644
> --- a/drivers/dma/tegra20-apb-dma.c
> +++ b/drivers/dma/tegra20-apb-dma.c
> @@ -814,7 +814,7 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
>  	unsigned int residual;
>  
>  	ret = dma_cookie_status(dc, cookie, txstate);
> -	if (ret == DMA_COMPLETE)
> +	if (ret == DMA_COMPLETE || !txstate)
>  		return ret;

Thanks for reporting this. I agree that we should not do this, however, 
looking at the code for Tegra, I am wondering if this could change the
actual state that is returned. Looking at dma_cookie_status() it will
call dma_async_is_complete() which will return either DMA_COMPLETE or
DMA_IN_PROGRESS. It could be possible that the actual state for the
DMA transfer in the tegra driver is DMA_ERROR, so I am wondering if we
should do something like the following  ...

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index 01e316f73559..45edab7418d0 100644
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -822,13 +822,8 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
        /* Check on wait_ack desc status */
        list_for_each_entry(dma_desc, &tdc->free_dma_desc, node) {
                if (dma_desc->txd.cookie == cookie) {
-                       residual =  dma_desc->bytes_requested -
-                                       (dma_desc->bytes_transferred %
-                                               dma_desc->bytes_requested);
-                       dma_set_residue(txstate, residual);
                        ret = dma_desc->dma_status;
-                       spin_unlock_irqrestore(&tdc->lock, flags);
-                       return ret;
+                       goto found;
                }
        }
 
@@ -836,17 +831,23 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
        list_for_each_entry(sg_req, &tdc->pending_sg_req, node) {
                dma_desc = sg_req->dma_desc;
                if (dma_desc->txd.cookie == cookie) {
-                       residual =  dma_desc->bytes_requested -
-                                       (dma_desc->bytes_transferred %
-                                               dma_desc->bytes_requested);
-                       dma_set_residue(txstate, residual);
                        ret = dma_desc->dma_status;
-                       spin_unlock_irqrestore(&tdc->lock, flags);
-                       return ret;
+                       goto found;
                }
        }
 
-       dev_dbg(tdc2dev(tdc), "cookie %d does not found\n", cookie);
+       dev_warn(tdc2dev(tdc), "cookie %d not found\n", cookie);
+       spin_unlock_irqrestore(&tdc->lock, flags);
+       return ret;
+
+found:
+       if (txstate) {
+               residual = dma_desc->bytes_requested -
+                          (dma_desc->bytes_transferred %
+                           dma_desc->bytes_requested);
+               dma_set_residue(txstate, residual);
+       }
+
        spin_unlock_irqrestore(&tdc->lock, flags);
        return ret;
 }

Cheers
Jon

-- 
nvpublic