Re: [PATCH v4 2/4] drm/shmem-helper: Switch to vmf_insert_pfn

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi,

I'm not knowledgeable enougth to give this a full review. If you can 
just answer my questions, fell free to add an

Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

to the patch. :)

Am 13.07.21 um 22:51 schrieb Daniel Vetter:
> We want to stop gup, which isn't the case if we use vmf_insert_page

What is gup?

> and VM_MIXEDMAP, because that does not set pte_special.
>
> v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day)
>
> v3: add more depends on MMU. For usb drivers this is a bit awkward,
> but really it's correct: To be able to provide a contig mapping of
> buffers to userspace on !MMU platforms we'd need to use the cma
> helpers for these drivers on those platforms. As-is this wont work.
>
> Also not exactly sure why vm_insert_page doesn't go boom, because that
> definitely wont fly in practice since the pages are non-contig to
> begin with.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Maxime Ripard <mripard@xxxxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> ---
>   drivers/gpu/drm/Kconfig                | 2 +-
>   drivers/gpu/drm/drm_gem_shmem_helper.c | 4 ++--
>   drivers/gpu/drm/gud/Kconfig            | 2 +-
>   drivers/gpu/drm/tiny/Kconfig           | 4 ++--
>   drivers/gpu/drm/udl/Kconfig            | 1 +
>   5 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 0d372354c2d0..314eefa39892 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -211,7 +211,7 @@ config DRM_KMS_CMA_HELPER
>   
>   config DRM_GEM_SHMEM_HELPER
>   	bool
> -	depends on DRM
> +	depends on DRM && MMU
>   	help
>   	  Choose this if you need the GEM shmem helper functions
>   
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index d5e6d4568f99..296ab1b7c07f 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -542,7 +542,7 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
>   	} else {
>   		page = shmem->pages[page_offset];
>   
> -		ret = vmf_insert_page(vma, vmf->address, page);
> +		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
>   	}
>   
>   	mutex_unlock(&shmem->pages_lock);
> @@ -612,7 +612,7 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>   		return ret;
>   	}
>   
> -	vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
> +	vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND;
>   	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>   	if (shmem->map_wc)
>   		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> diff --git a/drivers/gpu/drm/gud/Kconfig b/drivers/gpu/drm/gud/Kconfig
> index 1c8601bf4d91..9c1e61f9eec3 100644
> --- a/drivers/gpu/drm/gud/Kconfig
> +++ b/drivers/gpu/drm/gud/Kconfig
> @@ -2,7 +2,7 @@
>   
>   config DRM_GUD
>   	tristate "GUD USB Display"
> -	depends on DRM && USB
> +	depends on DRM && USB && MMU
>   	select LZ4_COMPRESS
>   	select DRM_KMS_HELPER
>   	select DRM_GEM_SHMEM_HELPER

I'm a kconfig noob, so this is rather a question than a review comment:



If DRM_GEM_SHMEM_HELPER already depends on MMU, this select will fail on 
non-MMU platforms? Why does the driver also depend on MMU? Simply to 
make the item disappear in menuconfig?

Best regards
Thomas

> diff --git a/drivers/gpu/drm/tiny/Kconfig b/drivers/gpu/drm/tiny/Kconfig
> index 5593128eeff9..c11fb5be7d09 100644
> --- a/drivers/gpu/drm/tiny/Kconfig
> +++ b/drivers/gpu/drm/tiny/Kconfig
> @@ -44,7 +44,7 @@ config DRM_CIRRUS_QEMU
>   
>   config DRM_GM12U320
>   	tristate "GM12U320 driver for USB projectors"
> -	depends on DRM && USB
> +	depends on DRM && USB && MMU
>   	select DRM_KMS_HELPER
>   	select DRM_GEM_SHMEM_HELPER
>   	help
> @@ -53,7 +53,7 @@ config DRM_GM12U320
>   
>   config DRM_SIMPLEDRM
>   	tristate "Simple framebuffer driver"
> -	depends on DRM
> +	depends on DRM && MMU
>   	select DRM_GEM_SHMEM_HELPER
>   	select DRM_KMS_HELPER
>   	help
> diff --git a/drivers/gpu/drm/udl/Kconfig b/drivers/gpu/drm/udl/Kconfig
> index 1f497d8f1ae5..c744175c6992 100644
> --- a/drivers/gpu/drm/udl/Kconfig
> +++ b/drivers/gpu/drm/udl/Kconfig
> @@ -4,6 +4,7 @@ config DRM_UDL
>   	depends on DRM
>   	depends on USB
>   	depends on USB_ARCH_HAS_HCD
> +	depends on MMU
>   	select DRM_GEM_SHMEM_HELPER
>   	select DRM_KMS_HELPER
>   	help

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

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