Re: [PATCH for-5.3] drm/omap: ensure we have a valid dma_mask

[Tomi Valkeinen]

On 09/08/2019 11:07, Christoph Hellwig wrote:
> On Fri, Aug 09, 2019 at 09:40:32AM +0300, Tomi Valkeinen wrote:
>> We do call dma_set_coherent_mask() in omapdrm's probe() (in omap_drv.c),
>> but apparently that's not enough anymore. Changing that call to
>> dma_coerce_mask_and_coherent() removes the WARN. I can create a patch for
>> that, or Christoph can respin this one.
> 
> Oh, yes - that actually is the right thing to do here.  If you already
> have it please just send it out.
> 
>>
>> I am not too familiar with the dma mask handling, so maybe someone can
>> educate:
>>
>> dma_coerce_mask_and_coherent() overwrites dev->dma_mask. Isn't that a bad
>> thing? What if the platform has set dev->dma_mask, and the driver
>> overwrites it with its value? Or who is supposed to set dev->dma_mask?
> 
> ->dma_mask is a complete mess.  It is a pointer when it really should
> just be a u64, and that means every driver layer has to allocate space
> for it.  We don't really do that for platform_devices, as that breaks
> horribly assumptions in the usb code.  That is why
> dma_coerce_mask_and_coherent exists as a nasty workaround that sets
> the dma_mask to the coherent_dma_mask for devices that don't have
> space for ->dma_mask allocated, which works as long as the device
> doesn't have differnet addressing requirements for both.
> 
> I'm actually working to fix that mess up at the moment, but it is going
> to take a few cycles until everything falls into place.

Alright, thanks for the clarification!

Here's my version.