Hi Gerd
Am 17.09.19 um 10:34 schrieb Gerd Hoffmann:
> On Fri, Sep 13, 2019 at 03:05:34PM +0200, Thomas Zimmermann wrote:
>
>>> +void ttm_bo_mmap_vma_setup(struct ttm_buffer_object *bo, struct vm_area_struct *vma)
>>> +{
>>> + vma->vm_ops = &ttm_bo_vm_ops;
>>> +
>>> + /*
>>> + * Note: We're transferring the bo reference to
>>> + * vma->vm_private_data here.
>>> + */
>>> +
>>> + vma->vm_private_data = bo;
>>> +
>>> + /*
>>> + * We'd like to use VM_PFNMAP on shared mappings, where
>>> + * (vma->vm_flags & VM_SHARED) != 0, for performance reasons,
>>> + * but for some reason VM_PFNMAP + x86 PAT + write-combine is very
>>> + * bad for performance. Until that has been sorted out, use
>>> + * VM_MIXEDMAP on all mappings. See freedesktop.org bug #75719
>>> + */
>>> + vma->vm_flags |= VM_MIXEDMAP;
>>> + vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
>>> +}
>>> +EXPORT_SYMBOL(ttm_bo_mmap_vma_setup);
>>
>> To me, this function looks like an internal helper that should rather
>> remain internal.
>
> Well, I'm moving that to a helper exactly to avoid drm gem ttm helpers
> messing with ttm internals. To not them initialize vm_flags for
> example, and to avoid exporting ttm_bo_vm_ops. Also to make sure ttm bo
> vma's are initialized the same way no matter which code path was taken
> to mmap the object.
It may not be worth blocking on this, so
Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
But I still think it's not a good interface because it exposes internal
details.
Please consider another idea: how about splitting off the ttm_bo_get()
and vma-flags setup of ttm_fbdev_mmap() into a separate function, like this:
void ttm_bo_mmap_refed(vma, bo)
{
ttm_bo_get(bo)
ttm_bo_mmap_vma_setup(vma);
}
EXPORT_SYMBOL(ttm_bo_mmap_refed)
int ttm_fbdev_mmap(vma, bo)
{
if (vma->vm_pgoff != 0)
return -EACCES;
ttm_bo_mmap_refed(vma, bo);
return 0;
}
That would allow to keep _vma_setup() an internal function.
ttm_fbdev_mmap() sounds like it is only for fbdev and the only user is
amdgpu. Can it be moved out of ttm entirely?
Best regards
Thomas
>> As mentioned in my reply to patch 5, maybe re-using
>> ttm_fbdev_mmap() could help.
>
> No, the check in that function prevents that from working.
>
> cheers,
> Gerd
>
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--
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
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