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

Jon Hunter
2016-06-08T08:51:57Z

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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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