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=ham 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 0999FC433E0 for ; Wed, 24 Feb 2021 15:21:58 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 51C6764E83 for ; Wed, 24 Feb 2021 15:21:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 51C6764E83 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=rowland.harvard.edu Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 253516EACA; Wed, 24 Feb 2021 15:21:56 +0000 (UTC) Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by gabe.freedesktop.org (Postfix) with SMTP id 123466EACA for ; Wed, 24 Feb 2021 15:21:54 +0000 (UTC) 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 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-Disposition: inline In-Reply-To: <20210224092304.29932-1-tzimmermann@suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: airlied@linux.ie, gregkh@linuxfoundation.org, Christoph Hellwig , hdegoede@redhat.com, dri-devel@lists.freedesktop.org, stable@vger.kernel.org, sean@poorly.run, christian.koenig@amd.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel