[PATCH] drm/ttm: Use ttm_bo_default_io_mem_pfn if io_mem_pfn is NULL

[Sean Paul]

On Wed, Nov 29, 2017 at 04:40:18PM +0100, Christian König wrote:
> Am 29.11.2017 um 16:36 schrieb Sean Paul:
> > On Wed, Nov 29, 2017 at 04:24:21PM +0100, Christian König wrote:
> > > Am 29.11.2017 um 16:20 schrieb Michal Srb:
> > > > The io_mem_pfn field was added in commit ea642c3216cb2a60d1c0e760ae47ee85c9c16447
> > > > and is called unconditionally. However, not all drivers were updated to set it.
> > > > 
> > > > Use the ttm_bo_default_io_mem_pfn function if a driver did not set its own.
> > > > 
> > > > Signed-off-by: Michal Srb <msrb at suse.com>
> > > NAK, when we have drivers missing this we should set this in the driver and
> > > not add the workaround here.
> > Why? What's the benefit in adding the same hook in 10 drivers (I was hoping
> > Michal would also remove the token .io_mem_pfn = ttm_bo_default_io_mem_pfn from
> > those as well)?
> 
> Not have this extra check in common TTM code? That is seriously bad coding
> style.
> 

[citation neeeded]

I'd argue it's bad form to require everyone add a copypasta hook to their driver
everytime an unrelated driver needs more control than the default gives :-)

I think your point would hold if we were talking about a couple of drivers, but
once you scale to 10+, it's no longer a trivial amount of code. If the null check
is too distracting, you could always pull it out into an inline.

Sean


> We have tons of fallbacks like this and I unfortunately even created new one
> without realizing that this is a problem.
> 
> But this really clutters the TTM code and makes it harder to understand.
> 
> Christian.
> 
> > 
> > Sean
> > 
> > > Which driver is missing this? I thought I fixed all of them.
> > > 
> > > Regards,
> > > Christian.
> > > 
> > > > ---
> > > >    drivers/gpu/drm/ttm/ttm_bo_vm.c | 5 ++++-
> > > >    1 file changed, 4 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > index c8ebb757e36b..e25a99bc519d 100644
> > > > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > @@ -234,7 +234,10 @@ static int ttm_bo_vm_fault(struct vm_fault *vmf)
> > > >    		if (bo->mem.bus.is_iomem) {
> > > >    			/* Iomem should not be marked encrypted */
> > > >    			cvma.vm_page_prot = pgprot_decrypted(cvma.vm_page_prot);
> > > > -			pfn = bdev->driver->io_mem_pfn(bo, page_offset);
> > > > +			if (bdev->driver->io_mem_pfn)
> > > > +				pfn = bdev->driver->io_mem_pfn(bo, page_offset);
> > > > +			else
> > > > +				pfn = ttm_bo_default_io_mem_pfn(bo, page_offset);
> > > >    		} else {
> > > >    			page = ttm->pages[page_offset];
> > > >    			if (unlikely(!page && i == 0)) {
> > > _______________________________________________
> > > dri-devel mailing list
> > > dri-devel at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS