Hi Am 23.02.21 um 14:44 schrieb Takashi Iwai:
On Tue, 23 Feb 2021 11:58:42 +0100, Thomas Zimmermann wrote:USB devices cannot perform DMA and hence have no dma_mask set in their device structure. Importing dmabuf into a USB-based driver fails, which break joining and mirroring of display in X11. For USB devices, pick the associated USB controller as attachment device, so that it can perform DMA. If the DMa controller does not support DMA transfers, we're aout of luck and cannot import. 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. 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") Cc: Christoph Hellwig <hch@xxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Johan Hovold <johan@xxxxxxxxxx> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Cc: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> Cc: Oliver Neukum <oneukum@xxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # v5.10+ --- drivers/gpu/drm/drm_prime.c | 36 ++++++++++++++++++++++++++++++ drivers/gpu/drm/tiny/gm12u320.c | 2 +- drivers/gpu/drm/udl/udl_drv.c | 2 +- include/drm/drm_gem_shmem_helper.h | 13 +++++++++++ include/drm/drm_prime.h | 5 +++++ 5 files changed, 56 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 2a54f86856af..9015850f2160 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -29,6 +29,7 @@ #include <linux/export.h> #include <linux/dma-buf.h> #include <linux/rbtree.h> +#include <linux/usb.h> #include <drm/drm.h> #include <drm/drm_drv.h> @@ -1055,3 +1056,38 @@ void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg) dma_buf_put(dma_buf); } EXPORT_SYMBOL(drm_prime_gem_destroy); + +/** + * drm_gem_prime_import_usb - helper library implementation of the import callback for USB devices + * @dev: drm_device to import into + * @dma_buf: dma-buf object to import + * + * This is an implementation of drm_gem_prime_import() for USB-based devices. + * USB devices cannot perform DMA directly. This function selects the USB host + * controller as DMA device instead. Drivers can use this as their + * &drm_driver.gem_prime_import implementation. + * + * See also drm_gem_prime_import(). + */ +#ifdef CONFIG_USB +struct drm_gem_object *drm_gem_prime_import_usb(struct drm_device *dev, + struct dma_buf *dma_buf) +{ + struct usb_device *udev; + struct device *usbhost; + + if (dev->dev->bus != &usb_bus_type) + return ERR_PTR(-ENODEV); + + udev = interface_to_usbdev(to_usb_interface(dev->dev)); + if (!udev->bus) + return ERR_PTR(-ENODEV); + + usbhost = udev->bus->controller;Aside from the discussion whether this "workaround" is needed, the use of udev->bus->controller here looks a bit suspicious. As the old USB code (before the commit 6eb0233ec2d0) indicated, it was rather usb->bus->sysdev that was used for the DMA mask, and it's also the one most of USB core code refers to. A similar question came up while fixing the same kind of bug in the media subsystem, and we concluded that bus->sysdev is a better choice.
Good to hear that we're not the only ones affected by this. Wrt the original code, using sysdev makes even more sense.
Best regards Thomas
Takashi _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
-- 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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