Messages in this thread | | | Date | Wed, 1 Dec 2021 14:18:53 +0000 | Subject | Re: [PATCH v2 3/3] drm/etnaviv: use a 32 bit mask as coherent DMA mask | From | Robin Murphy <> |
| |
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.
| |