From: Thomas Zimmermann <tzimmermann@suse.de>
To: "Noralf Trønnes" <noralf@tronnes.org>,
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,
stern@rowland.harvard.edu, dan.carpenter@oracle.com
Cc: dri-devel@lists.freedesktop.org, Pavel Machek <pavel@ucw.cz>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
Christoph Hellwig <hch@lst.de>,
stable@vger.kernel.org
Subject: Re: [PATCH v7] drm: Use USB controller's DMA mask when importing dmabufs
Date: Wed, 3 Mar 2021 14:27:32 +0100 [thread overview]
Message-ID: <6689d8d4-2686-e16e-339a-6d95f6e98dab@suse.de> (raw)
In-Reply-To: <f1271ed4-1bb1-0fe6-a5b1-db9dbae575fe@tronnes.org>
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Hi,
thanks for reviewing. This will be fixed in the next iteration.
Best regards
Thomas
Am 03.03.21 um 11:58 schrieb Noralf Trønnes:
>
>
> 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@suse.de>
>> Fixes: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices")
>> Tested-by: Pavel Machek <pavel@ucw.cz>
>> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Acked-by: Christian König <christian.koenig@amd.com>
>> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: <stable@vger.kernel.org> # v5.10+
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>> ---
>> 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;
--
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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prev parent reply other threads:[~2021-03-03 13:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-03 8:45 [PATCH v7] drm: Use USB controller's DMA mask when importing dmabufs Thomas Zimmermann
2021-03-03 10:58 ` Noralf Trønnes
2021-03-03 13:27 ` Thomas Zimmermann [this message]
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