Re: [PATCH 2/2] drm/msm: gpu: don't abuse dma_alloc for non-DMA allocations

[Jordan Crouse]

On Wed, Jul 26, 2017 at 05:52:45PM +0200, Arnd Bergmann wrote:
> In zap_shader_load_mdt(), we pass a pointer to a phys_addr_t
> into dmam_alloc_coherent, which the compiler warns about:
> 
> drivers/gpu/drm/msm/adreno/a5xx_gpu.c: In function 'zap_shader_load_mdt':
> drivers/gpu/drm/msm/adreno/a5xx_gpu.c:54:50: error: passing argument 3 of 'dmam_alloc_coherent' from incompatible pointer type [-Werror=incompatible-pointer-types]
> 
> The returned DMA address is later passed on to a function that
> takes a phys_addr_t, so it's clearly wrong to use the DMA
> mapping interface here: the memory may be uncached, or the
> address may be completely wrong if there is an IOMMU connected
> to the device. What the code actually wants to do is to get
> the physical address from the reserved-mem node. It goes through
> the dma-mapping interfaces for obscure reasons, and this
> apparently only works by chance, relying on specific bugs
> in the error handling of the arm64 dma-mapping implementation.
> 
> The same problem existed in the "venus" media driver, which was
> now fixed by Stanimir Varbanov after long discussions.
> 
> In order to make some progress here, I have now ported his
> approach over to the adreno driver. The patch is currently
> untested, and should get a good review, but it is now much
> simpler than the original, and it should be obvious what
> goes wrong if I made a mistake in the port.
> 
> See also: a6e2d36bf6b7 ("media: venus: don't abuse dma_alloc for non-DMA allocations")
> Cc: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx>
> Fixes: 7c65817e6d38 ("drm/msm: gpu: Enable zap shader for A5XX")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> I think we want this to be applied for 4.13, as the upstream
> code that was added in the merge window is seriously broken without it
> ---
>  drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 71 ++++++++++++-----------------------
>  drivers/gpu/drm/msm/adreno/a5xx_gpu.h |  2 -
>  2 files changed, 23 insertions(+), 50 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> index 1d54c76a7778..ce545b3a9d17 100644
> --- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
> @@ -15,7 +15,7 @@
>  #include <linux/cpumask.h>
>  #include <linux/qcom_scm.h>
>  #include <linux/dma-mapping.h>
> -#include <linux/of_reserved_mem.h>
> +#include <linux/of_address.h>
>  #include <linux/soc/qcom/mdt_loader.h>
>  #include "msm_gem.h"
>  #include "msm_mmu.h"
> @@ -29,6 +29,8 @@ static void a5xx_dump(struct msm_gpu *gpu);
>  static int zap_shader_load_mdt(struct device *dev, const char *fwname)
>  {
>  	const struct firmware *fw;
> +	struct device_node *np;
> +	struct resource r;
>  	phys_addr_t mem_phys;
>  	ssize_t mem_size;
>  	void *mem_region = NULL;
> @@ -37,6 +39,21 @@ static int zap_shader_load_mdt(struct device *dev, const char *fwname)
>  	if (!IS_ENABLED(CONFIG_ARCH_QCOM))
>  		return -EINVAL;
>  
> +	np = of_get_child_by_name(dev->of_node, "zap-shader");
> +	if (!np)
> +		return -ENODEV;
> +
> +	np = of_parse_phandle(dev->of_node, "memory-region", 0);

I think this should be np = of_parse_phandle(np, "memory-region", 0);

With that change this patch works great.

> @@ -373,44 +393,6 @@ static int a5xx_zap_shader_resume(struct msm_gpu *gpu)
>  }
>  
>  /* Set up a child device to "own" the zap shader */

This now incorrect comment can be zapped (pun intended).

> -static int a5xx_zap_shader_dev_init(struct device *parent, struct device *dev)
> -{
> -	struct device_node *node;
> -	int ret;
> -
> -	if (dev->parent)
> -		return 0;
> -

With above changes,
Acked-and-Tested-By: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>

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