Re: [PATCH/RFC 5/5] dmaengine: rcar-dmac: Widen DMA mask to 40 bits

[Magnus Damm <magnus.damm@gmail.com>]

Hi Geert,

On Fri, Nov 25, 2016 at 6:00 PM, Geert Uytterhoeven
<geert@linux-m68k.org> wrote:
> On Mon, Oct 31, 2016 at 6:08 PM, Geert Uytterhoeven
> <geert+renesas@glider.be> wrote:
>> By default, the DMA mask covers only the low 32-bit address space, which
>> causes SWIOTLB on arm64 to fall back to a bounce buffer for DMA
>> transfers involving memory outside the 32-bit address space.
>>
>> The R-Car DMA controller hardware supports a 40-bit address space, hence
>> widen the DMA mask to 40 bits to actually make use of this feature.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>
> Any comments? Thanks!
>
>> ---
>>  drivers/dma/sh/rcar-dmac.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
>> index 2e441d0ccd79a37a..93a69b992a51a7aa 100644
>> --- a/drivers/dma/sh/rcar-dmac.c
>> +++ b/drivers/dma/sh/rcar-dmac.c
>> @@ -1716,6 +1716,7 @@ static int rcar_dmac_probe(struct platform_device *pdev)
>>
>>         dmac->dev = &pdev->dev;
>>         platform_set_drvdata(pdev, dmac);
>> +       dma_set_mask_and_coherent(dmac->dev, DMA_BIT_MASK(40));

This makes sense to me since the hardware and the driver both can
access more than 32-bits of physical address space.

Cheers,

/ magnus