Den 03.03.2021 09.45, skrev Thomas Zimmermann:
> 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.
>
This doesn't seem to be the case anymore.
> Tested by joining/mirroring displays of udl and radeon un der Gnome/X11.
s/un der/under/
>
> v7:
> * fix use-before-init bug in gm12u320 (Dan)
> v6:
> * implement workaround in DRM drivers and hold reference to
> DMA device while USB device is in use
> * remove dev_is_usb() (Greg)
> * collapse USB helper into usb_intf_get_dma_device() (Alan)
> * integrate Daniel's TODO statement (Daniel)
> * fix typos (Greg)
> v5:
> * provide a helper for USB interfaces (Alan)
> * add FIXME item to documentation and TODO list (Daniel)
> v4:
> * implement workaround with USB helper functions (Greg)
> * use struct usb_device->bus->sysdev as DMA device (Takashi)
> v3:
> * drop gem_create_object
> * use DMA mask of USB controller, if any (Daniel, Christian, Noralf)
> v2:
> * move fix to importer side (Christian, Daniel)
> * update SHMEM and CMA helpers for new PRIME callbacks
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Fixes: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices")
> Tested-by: Pavel Machek <pavel@xxxxxx>
> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Acked-by: Christian König <christian.koenig@xxxxxxx>
> Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.10+
> Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> ---
> Documentation/gpu/todo.rst | 21 +++++++++++++++++++++
> drivers/gpu/drm/tiny/gm12u320.c | 28 ++++++++++++++++++++++++++--
> drivers/gpu/drm/udl/udl_drv.c | 17 +++++++++++++++++
> drivers/gpu/drm/udl/udl_drv.h | 1 +
> drivers/gpu/drm/udl/udl_main.c | 9 +++++++++
> drivers/usb/core/usb.c | 32 ++++++++++++++++++++++++++++++++
> include/linux/usb.h | 2 ++
> 7 files changed, 108 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/tiny/gm12u320.c b/drivers/gpu/drm/tiny/gm12u320.c
> index 0b4f4f2af1ef..4fe372f43cf5 100644
> --- a/drivers/gpu/drm/tiny/gm12u320.c
> +++ b/drivers/gpu/drm/tiny/gm12u320.c
[...]
> @@ -638,12 +656,15 @@ static int gm12u320_usb_probe(struct usb_interface *interface,
> struct gm12u320_device, dev);
> if (IS_ERR(gm12u320))
> return PTR_ERR(gm12u320);
> + dev = &gm12u320->dev;
> +
> + gm12u320->dmadev = usb_intf_get_dma_device(to_usb_interface(dev->dev));
> + if (!gm12u320->dmadev)
> + drm_warn(dev, "buffer sharing not supported"); /* not an error */
>
When implementing this in my own driver I discovered that this device
ref will leak if probing fails after this.
I've done it like this:
gdrm->dmadev = usb_intf_get_dma_device(intf);
if (!gdrm->dmadev)
dev_warn(dev, "buffer sharing not supported");
ret = drm_dev_register(drm, 0);
if (ret) {
put_device(gdrm->dmadev);
return ret;
}
An even better solution would be to have a devm_ version of the function.
Noralf.
> INIT_DELAYED_WORK(&gm12u320->fb_update.work, gm12u320_fb_update_work);
> mutex_init(&gm12u320->fb_update.lock);
>
> - dev = &gm12u320->dev;
> -
> ret = drmm_mode_config_init(dev);
> if (ret)
> return ret;
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