Re: [RFC 01/14] drm/i915: allocate gem memory for mipi dbi cmd buffer

Singh, Gaurav K
2015-06-16T17:10:00Z

On 6/15/2015 4:00 PM, Daniel Vetter wrote:
> On Mon, Jun 01, 2015 at 02:03:15PM +0300, Ville Syrjälä wrote:
>> On Fri, May 29, 2015 at 07:10:53PM +0200, Daniel Vetter wrote:
>>> On Fri, May 29, 2015 at 01:59:01PM +0300, Ville Syrjälä wrote:
>>>> On Fri, May 29, 2015 at 04:06:53PM +0530, Gaurav K Singh wrote:
>>>>> Allocate gem memory for MIPI DBI command buffer. This memory
>>>>> will be used when sending command via DBI interface.
>>>> Why would you allocate this via gem? AFAICS you only feed the bus
>>>> address to the hardware. Using the dma-api would seem like the right
>>>> choice here, but I'm not sure how to deal with the dma mask.
>>> Yeah dma_alloc_coherent is what you want here. The mask can be ignored,
>>> it should be suitable already.
>> Umm, this thing seems to limited to 32bit addresses. And we set the mask
>> to 39 or 40 bits depending on the gen.
> Well that's what we have dma_set_coherent_mask for, hooray. Not the first
> one, see the other hacks with comments in i915_driver_load.
> -Daniel
checking on the usage of dma_alloc_coherent. Will come back on this.

With regards,
Gaurav