linux-kernel - Re: Regression: 6eb0233ec2d0 ("usb: don't inherity DMA properties for USB devices")

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Date:   Thu, 18 Feb 2021 16:21:26 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...hat.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        USB list <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Regression: 6eb0233ec2d0 ("usb: don't inherity DMA properties for
 USB devices")

Hi

Am 18.02.21 um 16:07 schrieb Christoph Hellwig:
> On Thu, Feb 18, 2021 at 03:56:00PM +0100, Thomas Zimmermann wrote:
>> I only have udl devices, but I expect that other DRM USB adapters are also
>> affected.
> 
> Find where the driver calls dma_map_* itself instead of using the USB
> wrappers and fix that..
> 

Sure, it's at [1]. For udl, the dmabuf would need to be in system 
memory. The driver creates urbs from the framebuffer content and sends 
them to the device for displaying.

My question is more: what's the best interface to do this? Is there 
example code somewhere?

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/v5.11/source/drivers/gpu/drm/drm_prime.c#L630


-- 
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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