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

[Christian König]

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.

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)) {
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