RE: [RFC PATCH] mmc: renesas_sdhi_internal_dmac: fall back to PIO if scatterlist doesn't match

[Yoshihiro Shimoda]

Hi Wolfram-san,

Thank you for the patch!

> From: Wolfram Sang, Sent: Thursday, April 5, 2018 2:01 AM
> 
> From: Wolfram Sang 
> 
> If we detect an incompatible scatterlist, we should fall back to PIO,
> too.
> 
> Signed-off-by: Wolfram Sang 
> ---
> 
> I found this while working on the RX DMA issue. I don't see a reason why we
> shouldn't fall back in this case as well. But maybe I am missing something.
> 
> Shimoda-san: what do you think?
> 
>  drivers/mmc/host/renesas_sdhi_internal_dmac.c | 6 +-
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/mmc/host/renesas_sdhi_internal_dmac.c 
> b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> index 380570a26a09..561e90755a3b 100644
> --- a/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> +++ b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> @@ -161,11 +161,7 @@ renesas_sdhi_internal_dmac_start_dma(struct 
> tmio_mmc_host *host,
>   enum dma_data_direction dir;
>   int ret;
> 
> - /* This DMAC cannot handle if sg_len is not 1 */

I would like to keep this comment.

> - WARN_ON(host->sg_len > 1);
> -
> - /* This DMAC cannot handle if buffer is not 8-bytes alignment */
> - if (!IS_ALIGNED(sg->offset, 8))
> + if (WARN_ON(host->sg_len > 1) || !IS_ALIGNED(sg->offset, 8))

As Ulf-san said on other thread about this WARN_ON(),
I think dropping the WARN_ON() is better.

Best regards,
Yoshihiro Shimoda

Re: [RFC PATCH] mmc: renesas_sdhi_internal_dmac: fall back to PIO if scatterlist doesn't match

[Wolfram Sang]

> > -   /* This DMAC cannot handle if sg_len is not 1 */
> > -   WARN_ON(host->sg_len > 1);
> > -
> > -   /* This DMAC cannot handle if buffer is not 8-bytes alignment */
> > -   if (!IS_ALIGNED(sg->offset, 8))
> > +   if (WARN_ON(host->sg_len > 1) || !IS_ALIGNED(sg->offset, 8))
> 
> The WARN_ON becomes a bit misleading being a part of the if statement,
> as it should never happen when the driver has set ->max_segs = 1.

Uh, yeah, right. So, we could simply drop the WARN_ON?



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Re: [RFC PATCH] mmc: renesas_sdhi_internal_dmac: fall back to PIO if scatterlist doesn't match

[Ulf Hansson]

On 4 April 2018 at 19:00, Wolfram Sang  wrote:
> From: Wolfram Sang 
>
> If we detect an incompatible scatterlist, we should fall back to PIO,
> too.
>
> Signed-off-by: Wolfram Sang 
> ---
>
> I found this while working on the RX DMA issue. I don't see a reason why we
> shouldn't fall back in this case as well. But maybe I am missing something.
>
> Shimoda-san: what do you think?
>
>  drivers/mmc/host/renesas_sdhi_internal_dmac.c | 6 +-
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/host/renesas_sdhi_internal_dmac.c 
> b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> index 380570a26a09..561e90755a3b 100644
> --- a/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> +++ b/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> @@ -161,11 +161,7 @@ renesas_sdhi_internal_dmac_start_dma(struct 
> tmio_mmc_host *host,
> enum dma_data_direction dir;
> int ret;
>
> -   /* This DMAC cannot handle if sg_len is not 1 */
> -   WARN_ON(host->sg_len > 1);
> -
> -   /* This DMAC cannot handle if buffer is not 8-bytes alignment */
> -   if (!IS_ALIGNED(sg->offset, 8))
> +   if (WARN_ON(host->sg_len > 1) || !IS_ALIGNED(sg->offset, 8))

The WARN_ON becomes a bit misleading being a part of the if statement,
as it should never happen when the driver has set ->max_segs = 1.

For the alignment check, and the moving to PIO, this certainly makes
sense to me.

> goto force_pio;
>
> if (data->flags & MMC_DATA_READ) {

Kind regards
Uffe