[PATCH v3] drm: Use USB controller's DMA mask when importing dmabufs

[Thomas Zimmermann]

Hi

Am 23.02.21 um 18:30 schrieb Greg KH:
> On Tue, Feb 23, 2021 at 11:00:54AM -0500, Alan Stern wrote:
>> On Tue, Feb 23, 2021 at 03:06:07PM +0100, Thomas Zimmermann wrote:
>>> Hi
>>>
>>> Am 23.02.21 um 14:44 schrieb Takashi Iwai:
>>
>>>> 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.
>>
>> Hmmm, I had forgotten about this.  So DMA masks aren't inherited after
>> all, thanks to commit 6eb0233ec2d0.  That leas me to wonder how well
>> usb-storage is really working these days...
>>
>> The impression I get is that Greg would like the USB core to export a
>> function which takes struct usb_interface * as argument and returns the
>> appropriate DMA mask value.  Then instead of messing around with USB
>> internals, drm_gem_prime_import_usb could just call this new function.
>>
>> Adding such a utility function would be a sufficiently small change that
>> it could go into the -stable kernels with no trouble.
> 
> Yes, sorry for not being clear, that is what I think would make the most
> sense, then all USB drivers could use it easily and it can be changed in
> one location if the DMA logic ever changes.

We can certainly do that. Thanks for clarifying. I'll send out an 
updated patch soon.

Best regards
Thomas

> 
> thanks,
> 
> greg k-h
> _______________________________________________
> dri-devel mailing list
> dri-devel at lists.freedesktop.org
> 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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20210224/1230542e/attachment.sig>