From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E680DC433DB for ; Wed, 24 Feb 2021 15:27:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8735364ECB for ; Wed, 24 Feb 2021 15:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233299AbhBXP0K (ORCPT ); Wed, 24 Feb 2021 10:26:10 -0500 Received: from netrider.rowland.org ([192.131.102.5]:47623 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S235751AbhBXPWs (ORCPT ); Wed, 24 Feb 2021 10:22:48 -0500 Received: (qmail 1308142 invoked by uid 1000); 24 Feb 2021 10:21:53 -0500 Date: Wed, 24 Feb 2021 10:21:53 -0500 From: Alan Stern To: Thomas Zimmermann Cc: daniel@ffwll.ch, airlied@linux.ie, maarten.lankhorst@linux.intel.com, mripard@kernel.org, sumit.semwal@linaro.org, christian.koenig@amd.com, gregkh@linuxfoundation.org, hdegoede@redhat.com, sean@poorly.run, noralf@tronnes.org, dri-devel@lists.freedesktop.org, Christoph Hellwig , stable@vger.kernel.org Subject: Re: [PATCH v4] drm: Use USB controller's DMA mask when importing dmabufs Message-ID: <20210224152153.GA1307460@rowland.harvard.edu> References: <20210224092304.29932-1-tzimmermann@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210224092304.29932-1-tzimmermann@suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Feb 24, 2021 at 10:23:04AM +0100, Thomas Zimmermann wrote: > 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. > > 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 > Fixes: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices") > Cc: Christoph Hellwig > Cc: Greg Kroah-Hartman > Cc: # v5.10+ > --- > +struct drm_gem_object *drm_gem_prime_import_usb(struct drm_device *dev, > + struct dma_buf *dma_buf) > +{ > + struct usb_device *udev; > + struct device *dmadev; > + struct drm_gem_object *obj; > + > + if (!dev_is_usb(dev->dev)) > + return ERR_PTR(-ENODEV); > + udev = interface_to_usbdev(to_usb_interface(dev->dev)); > + > + dmadev = usb_get_dma_device(udev); You can do it this way if you want, but I think usb_get_dma_device would be easier to use if its argument was a pointer to struct usb_interface or (even better) a pointer to a usb_interface's embedded struct device. Then you wouldn't need to compute udev, and the same would be true for other callers. Alan Stern