lkml.org 
[lkml]   [2021]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v2 3/3] drm/etnaviv: use a 32 bit mask as coherent DMA mask
From
On 2021-12-01 13:41, Lucas Stach wrote:
> Hi Robin,
>
> Am Mittwoch, dem 01.12.2021 um 12:50 +0000 schrieb Robin Murphy:
>> Sorry I missed this earlier...
>>
>> On 2021-09-07 17:49, Michael Walle wrote:
>>> The STLB and the first command buffer (which is used to set up the TLBs)
>>> has a 32 bit size restriction in hardware. There seems to be no way to
>>> specify addresses larger than 32 bit. Keep it simple and restict the
>>> addresses to the lower 4 GiB range for all coherent DMA memory
>>> allocations.
>>>
>>> Please note, that platform_device_alloc() will initialize dev->dma_mask
>>> to point to pdev->platform_dma_mask, thus dma_set_mask() will work as
>>> expected.
>>>
>>> While at it, move the dma_mask setup code to the of_dma_configure() to
>>> keep all the DMA setup code next to each other.
>>>
>>> Suggested-by: Lucas Stach <l.stach@pengutronix.de>
>>> Signed-off-by: Michael Walle <michael@walle.cc>
>>> ---
>>> drivers/gpu/drm/etnaviv/etnaviv_drv.c | 20 ++++++++++++++++++--
>>> 1 file changed, 18 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>>> index 54eb653ca295..0b756ecb1bc2 100644
>>> --- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>>> +++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
>>> @@ -613,6 +613,24 @@ static int etnaviv_pdev_probe(struct platform_device *pdev)
>>> component_match_add(dev, &match, compare_str, names[i]);
>>> }
>>>
>>> + /*
>>> + * PTA and MTLB can have 40 bit base addresses, but
>>> + * unfortunately, an entry in the MTLB can only point to a
>>> + * 32 bit base address of a STLB. Moreover, to initialize the
>>> + * MMU we need a command buffer with a 32 bit address because
>>> + * without an MMU there is only an indentity mapping between
>>> + * the internal 32 bit addresses and the bus addresses.
>>> + *
>>> + * To make things easy, we set the dma_coherent_mask to 32
>>> + * bit to make sure we are allocating the command buffers and
>>> + * TLBs in the lower 4 GiB address space.
>>> + */
>>> + if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(40)) ||
>>> + dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32))) {
>>
>> Since AFAICS you're not changing the default dma_mask pointer to point
>> to some storage other than the coherent mask, the dma_set_mask() call
>> effectively does nothing and both masks will end up reading back as 32 bits.
>>
> From what I can see the dma_mask has allocated storage in the platform
> device and does not point to the coherent dma mask, see
> setup_pdev_dma_masks().

Urgh, apologies for the confusion - seems I had one of those mental
short-circuits and was utterly convinced that that's what the platform
device setup did, but of course it's only the fallback case in
of_dma_configure(). Sorry for the noise!

Cheers,
Robin.

\
 
 \ /
  Last update: 2021-12-01 15:20    [W:0.037 / U:0.552 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site