Re: [PATCH v2 3/3] drm/etnaviv: use a 32 bit mask as coherent DMA mask

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.

Robin.

• dev_dbg(&pdev->dev, "No suitable DMA available\n");
  

• return -ENODEV;
  

• }
• /*
  • Apply the same DMA configuration to the virtual etnaviv
  • device as the GPU we found. This assumes that all Vivante

@@ -671,8 +689,6 @@ static int __init etnaviv_init(void) of_node_put(np); goto unregister_platform_driver; }

• pdev->dev.coherent_dma_mask = DMA_BIT_MASK(40);
  

• pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
  
  

  ret = platform_device_add(pdev); if (ret) {