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RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:url,suse.de:dkim,suse.de:mid,suse.de:email] X-Rspamd-Queue-Id: B52B44D1F1 X-Spam-Flag: NO X-Spam-Score: -4.51 X-Spam-Level: Hi Am 27.03.26 um 10:38 schrieb Chen-Yu Tsai: > On Fri, Mar 27, 2026 at 3:21 PM Thomas Zimmermann wrote: >> Hi >> >> Am 26.03.26 um 11:01 schrieb Chen-Yu Tsai: >>> From: Rob Herring >>> >>> Introduce a new flag, DRM_MODE_DUMB_KERNEL_MAP, for struct >>> drm_mode_create_dumb. This flag is for internal kernel use to indicate >>> if dumb buffer allocation needs a kernel mapping. This is needed only for >>> GEM DMA where creating a kernel mapping or not has to be decided at >>> allocation time because creating a mapping on demand (with vmap()) is not >>> guaranteed to work. >> I still don't understand what you're trying to achieve. As I pointed >> out, ever driver's memory manager potentially requires a vmap. Passing >> around flags will not solve that problem. If vmap is not possible, the >> driver should not provide the vmap callbacks in the first place. > I'm trying to convert the Rockchip and Exynos drivers to the GEM DMA Ok. > helpers. Both have their reasons for not using the helpers, one of them > being that the DRM device is not the DMA device. This is already fixed > by my other series. Both drivers also set DMA_ATTR_NO_KERNEL_MAPPING > for buffer allocations other than the one used by fb_helper. > > Exynos's GEM implementation also sets extra DMA attributes at the > allocation phase for their custom GEM create ioctl. But otherwise > exynos is just reimplementing all the GEM DMA helpers in almost > identical fashion. And to your point, exynos does not provide the > vmap callback. > > Rockchip's GEM implementation splits the code path between DMA and > IOMMU usage as it needs to attach and detach the DMA device from the > IOMMU domain on the fly. This predates the DMA IOMMU framework. This > GEM implementation provides the vmap callback, which will fail for > direct DMA allocations without the kernel mapping. > > There's also something fishy about Rockchip's DRM driver. It's using > fbdev-dma, even though it's not based on the GEM DMA helpers or even > drm_gem_dma_object. Oh! > > As you are against changing the existing *_dumb_create() interface, > I will look into reusing drm_gem_dma_object with driver-specific > functions. I believe I will need to keep patch 2 adding dma_attrs > though. Would that be acceptable? I think so. Sharing code is good, but I don't like these flags that change a function's overall behavior. I think that's the case here. Flags are OK when they extent or modify a little detail, but extensively used the affected code becomes unmaintainable. It's better to have a dedicated function for such special cases. What you could do is to provide a separate helper that allocates an object with the specific vmap behavior and use it for these drivers. The allocator function should also set dedicated gem-object funcs w/o vmap/vunmap where possible.  Drivers can then pick the helpers. If you 're looking for an example, take a look at commit 660cd44659a0 ("drm/shmem-helper: Import dmabuf without mapping its sg_table")  and it's patch series.  With gem-shmem, many drivers don't work correctly with the sg-table imported.  The commit provides them with a separate import helper that takes care of this. Best regards Thomas > > Once again, thank you for your patience. > > > ChenYu > > >> Best regards >> Thomas >> >>> Several drivers are using reimplementing the GEM DMA helpers because >>> they distinguish between kernel and userspace allocations to create a >>> kernel mapping or not. Adding a flag allows migrating these drivers >>> to the helpers while preserving their existing behavior. These include >>> exynos, rockchip, and previously mediatek. >>> >>> Update the callers of drm_mode_dumb_create() to set >>> drm_mode_dumb_create.flags to appropriate defaults. Currently, flags can >>> be set to anything by userspace, but is unused within the kernel. Let's >>> force flags to zero (no kernel mapping) for userspace callers by default. >>> For in kernel clients, set DRM_MODE_DUMB_KERNEL_MAP by default. Drivers >>> can override this as needed. >>> >>> Signed-off-by: Rob Herring >>> [wenst@chromium.org: Emit warning (once) if args->flags is not zero] >>> [wenst@chromium.org: Moved flag def. to include/drm/drm_dumb_buffers.h] >>> Signed-off-by: Chen-Yu Tsai >>> --- >>> Changes since v2: >>> - Switched to drm_warn_once() >>> - Moved flag definition from include/uapi/ to include/drm/drm_dumb_buffers.h >>> - Reworded commit message >>> >>> Changes since v1: >>> - Emit warning if args->flags is not zero >>> --- >>> drivers/gpu/drm/drm_client.c | 2 ++ >>> drivers/gpu/drm/drm_dumb_buffers.c | 4 ++++ >>> include/drm/drm_dumb_buffers.h | 3 +++ >>> 3 files changed, 9 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c >>> index 46c465bce98c..3d3e61823cc1 100644 >>> --- a/drivers/gpu/drm/drm_client.c >>> +++ b/drivers/gpu/drm/drm_client.c >>> @@ -14,6 +14,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -404,6 +405,7 @@ drm_client_buffer_create_dumb(struct drm_client_dev *client, u32 width, u32 heig >>> dumb_args.width = width; >>> dumb_args.height = height; >>> dumb_args.bpp = drm_format_info_bpp(info, 0); >>> + dumb_args.flags = DRM_MODE_DUMB_KERNEL_MAP; >>> ret = drm_mode_create_dumb(dev, &dumb_args, client->file); >>> if (ret) >>> return ERR_PTR(ret); >>> diff --git a/drivers/gpu/drm/drm_dumb_buffers.c b/drivers/gpu/drm/drm_dumb_buffers.c >>> index e2b62e5fb891..60f4c2d08641 100644 >>> --- a/drivers/gpu/drm/drm_dumb_buffers.c >>> +++ b/drivers/gpu/drm/drm_dumb_buffers.c >>> @@ -233,6 +233,10 @@ int drm_mode_create_dumb_ioctl(struct drm_device *dev, >>> struct drm_mode_create_dumb *args = data; >>> int err; >>> >>> + if (args->flags) >>> + drm_warn_once(dev, "drm_mode_create_dumb.flags is not zero.\n"); >>> + args->flags = 0; >>> + >>> err = drm_mode_create_dumb(dev, args, file_priv); >>> if (err) { >>> args->handle = 0; >>> diff --git a/include/drm/drm_dumb_buffers.h b/include/drm/drm_dumb_buffers.h >>> index 1f3a8236fb3d..4657e44533f4 100644 >>> --- a/include/drm/drm_dumb_buffers.h >>> +++ b/include/drm/drm_dumb_buffers.h >>> @@ -6,6 +6,9 @@ >>> struct drm_device; >>> struct drm_mode_create_dumb; >>> >>> +/* drm_mode_create_dumb flags for internal use */ >>> +#define DRM_MODE_DUMB_KERNEL_MAP (1<<0) >>> + >>> int drm_mode_size_dumb(struct drm_device *dev, >>> struct drm_mode_create_dumb *args, >>> unsigned long hw_pitch_align, >> -- >> -- >> Thomas Zimmermann >> Graphics Driver Developer >> SUSE Software Solutions Germany GmbH >> Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com >> GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg) >> >> -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)