Re: [PATCH v4] drm: Use USB controller's DMA mask when importing dmabufs

Pavel Machek
2021-02-25T09:48:08Z

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Hi!

> USB devices cannot perform DMA and hence have no dma_mask set in their
> device structure. Therefore importing dmabuf into a USB-based driver
> fails, which breaks joining and mirroring of display in X11.
>
> For USB devices, pick the associated USB controller as attachment device.
> This allows the DRM import helpers to perform the DMA setup. If the DMA
> controller does not support DMA transfers, we're out of luck and cannot
> import. Our current USB-based DRM drivers don't use DMA, so the actual
> DMA device is not important.
>
> Drivers should use DRM_GEM_SHMEM_DROVER_OPS_USB to initialize their
> instance of struct drm_driver.
>
> Tested by joining/mirroring displays of udl and radeon un der
> Gnome/X11.

Thanks for doing this.

Tested-by: Pavel Machek <pavel@ucw.cz>

Best regards,
Pavel
--
http://www.livejournal.com/~pavelmachek

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