[PATCH 1/2] drm/shmem: Use cached mappings by default

[Thomas Zimmermann]

Hi

Am 14.05.20 um 14:40 schrieb Daniel Vetter:
> On Wed, May 13, 2020 at 05:03:11PM +0200, Thomas Zimmermann wrote:
>> SHMEM-buffer backing storage is allocated from system memory; which is
>> typically cachable. Currently, only virtio uses cachable mappings; udl
>> uses its own vmap/mmap implementation for cachable mappings. Other
>> drivers default to writecombine mappings.
> 
> I'm pretty sure this breaks all these drivers. quick grep on a few
> functions says this is used by lima, panfrost, v3d. And they definitely
> need uncached/wc stuff afaiui. Or I'm completely missing something?

OK, I better get some testing for this code. :D

> -Daniel
> 
>>
>> Use cached mappings by default. The exception is pages imported via
>> dma-buf. DMA memory is usually not cached.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> ---
>>  drivers/gpu/drm/drm_gem_shmem_helper.c  | 6 ++++--
>>  drivers/gpu/drm/virtio/virtgpu_object.c | 1 -
>>  include/drm/drm_gem_shmem_helper.h      | 4 ++--
>>  3 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> index df31e5782eed1..1ce90325dfa31 100644
>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> @@ -259,7 +259,7 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
>>  	} else {
>>  		pgprot_t prot = PAGE_KERNEL;
>>  
>> -		if (!shmem->map_cached)
>> +		if (shmem->map_wc)
>>  			prot = pgprot_writecombine(prot);
>>  		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
>>  				    VM_MAP, prot);
>> @@ -546,7 +546,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>>  
>>  	vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
>>  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>> -	if (!shmem->map_cached)
>> +	if (shmem->map_wc)
>>  		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
>>  	vma->vm_ops = &drm_gem_shmem_vm_ops;
>>  
>> @@ -664,6 +664,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
>>  	if (IS_ERR(shmem))
>>  		return ERR_CAST(shmem);
>>  
>> +	shmem->map_wc = false; /* dma-buf mappings use writecombine */
>> +
>>  	shmem->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
>>  	if (!shmem->pages) {
>>  		ret = -ENOMEM;
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
>> index 6ccbd01cd888c..80ba6b2b61668 100644
>> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
>> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
>> @@ -132,7 +132,6 @@ struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
>>  
>>  	dshmem = &shmem->base.base;
>>  	dshmem->base.funcs = &virtio_gpu_shmem_funcs;
>> -	dshmem->map_cached = true;
>>  	return &dshmem->base;
>>  }
>>  
>> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
>> index 294b2931c4cc0..a5bc082a77c48 100644
>> --- a/include/drm/drm_gem_shmem_helper.h
>> +++ b/include/drm/drm_gem_shmem_helper.h
>> @@ -98,9 +98,9 @@ struct drm_gem_shmem_object {
>>  	unsigned int vmap_use_count;
>>  
>>  	/**
>> -	 * @map_cached: map object cached (instead of using writecombine).
>> +	 * @map_wc: map object using writecombine (instead of cached).
>>  	 */
>> -	bool map_cached;
>> +	bool map_wc;
>>  };
>>  
>>  #define to_drm_gem_shmem_obj(obj) \
>> -- 
>> 2.26.2
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 488 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20200514/87cde4ed/attachment-0001.sig>