Subject: Re: linux-next: build failure after merge of the drm tree

From: Paul Cercueil <[email-masked]>
Date: Wed, 30 Sep 2020 15:33:13 +0200

Hi Christoph,

Le mer. 30 sept. 2020 à 11:02, Christoph Hellwig <[email-masked]> a écrit 
:
> On Mon, Sep 28, 2020 at 03:31:28PM +0200, Paul Cercueil wrote:
>>  It's allocated with dma_alloc_wc, but then it's only accessed as
>>  non-coherent.
>> 
>>  Anyway, for the time being I guess you could revert 37054fc81443. 
>> But I
>>  have patches on top of it in drm-misc-next so it's going to be a 
>> mess.
>> 
>>  If we have time I can come up with a custom dumb_create() fonction, 
>> to make
>>  sure that the GEM buffers are allocated with 
>> dma_alloc_noncoherent(). Is
>>  there a dma_mmap_noncoherent() too?
> 
> Please use the lower-level dma_alloc_pages and then just insert the
> pages directly using remap_pfn_range.  Although it might make sense
> to eventually create a wrapper around remap_pfn_range for all the
> vma sizing sanity checks.

One thing missing for remap_pfn_range(), I have no alternative for this:

vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, 
DMA_ATTR_NON_CONSISTENT);

So I have to do:

vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
pgprot_val(vma->vm_page_prot) &= ~_CACHE_MASK;
pgprot_val(vma->vm_page_prot) |= _CACHE_CACHABLE_NONCOHERENT;

And that will only compile on MIPS, because these _CACHE_* macros are 
only defined there.

I would need something like a pgprot_noncoherent(), I think.

-Paul