[1/2] drm/msm: gpu: don't abuse dma_alloc for non-DMA allocations

Message ID 20170620201720.225593-1-arnd@arndb.de
State New
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  • [1/2] drm/msm: gpu: don't abuse dma_alloc for non-DMA allocations
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Commit Message

Arnd Bergmann June 20, 2017, 8:16 p.m.
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.

My interpretation is that using dmam_alloc_coherent() had two
purposes:

 a) get a chunk of consecutive memory that may be larger than
    the limit for kmalloc()

 b) use the devres infrastructure to simplify the unwinding
    in the error case.

I think ideally we'd use a devres-based version of
alloc_pages_exact() here, but since that doesn't exist,
let's use devm_get_free_pages() instead. This wastes a little
memory as the size gets rounded up to a power of two, but
is otherwise harmless. If we want to save memory here, calling
devm_free_pages() to release the memory once it is no longer
needed is probably better anyway.

Fixes: 7c65817e6d38 ("drm/msm: gpu: Enable zap shader for A5XX")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

-- 
2.9.0

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Comments

Jordan Crouse June 21, 2017, 2:53 p.m. | #1
On Tue, Jun 20, 2017 at 10:16:50PM +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.

> 

> My interpretation is that using dmam_alloc_coherent() had two

> purposes:

> 

>  a) get a chunk of consecutive memory that may be larger than

>     the limit for kmalloc()

> 

>  b) use the devres infrastructure to simplify the unwinding

>     in the error case.

> 

> I think ideally we'd use a devres-based version of

> alloc_pages_exact() here, but since that doesn't exist,

> let's use devm_get_free_pages() instead. This wastes a little

> memory as the size gets rounded up to a power of two, but

> is otherwise harmless. If we want to save memory here, calling

> devm_free_pages() to release the memory once it is no longer

> needed is probably better anyway.

> 

> Fixes: 7c65817e6d38 ("drm/msm: gpu: Enable zap shader for A5XX")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>


Seems reasonable to me if Bjorn agrees.

Acked-by: Jordan Crouse <jcrouse@codeaurora.org>


> ---

>  drivers/gpu/drm/msm/adreno/a5xx_gpu.c | 4 +++-

>  1 file changed, 3 insertions(+), 1 deletion(-)

> 

> diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c

> index b4b54f1c24bc..eee9ac81aaa1 100644

> --- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c

> +++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c

> @@ -51,11 +51,13 @@ static int zap_shader_load_mdt(struct device *dev, const char *fwname)

>  	}

>  

>  	/* Allocate memory for the firmware image */

> -	mem_region = dmam_alloc_coherent(dev, mem_size, &mem_phys, GFP_KERNEL);

> +	mem_region = (void *)devm_get_free_pages(dev, GFP_KERNEL,

> +			get_order(mem_size));

>  	if (!mem_region) {

>  		ret = -ENOMEM;

>  		goto out;

>  	}

> +	mem_phys = virt_to_phys(mem_region);

>  

>  	/* Load the rest of the MDT */

>  	ret = qcom_mdt_load(dev, fw, fwname, GPU_PAS_ID, mem_region, mem_phys,

> -- 

> 2.9.0

> 

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Patch

diff --git a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
index b4b54f1c24bc..eee9ac81aaa1 100644
--- a/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a5xx_gpu.c
@@ -51,11 +51,13 @@  static int zap_shader_load_mdt(struct device *dev, const char *fwname)
 	}
 
 	/* Allocate memory for the firmware image */
-	mem_region = dmam_alloc_coherent(dev, mem_size, &mem_phys, GFP_KERNEL);
+	mem_region = (void *)devm_get_free_pages(dev, GFP_KERNEL,
+			get_order(mem_size));
 	if (!mem_region) {
 		ret = -ENOMEM;
 		goto out;
 	}
+	mem_phys = virt_to_phys(mem_region);
 
 	/* Load the rest of the MDT */
 	ret = qcom_mdt_load(dev, fw, fwname, GPU_PAS_ID, mem_region, mem_phys,