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SubjectRe: [PATCH] gpu: drm: v3d: use new return type vm_fault_t
On Tue, Jul 03, 2018 at 09:40:43PM +0530, Souptick Joarder wrote:
> Use new return type vm_fault_t for fault handler. For
> now, this is just documenting that the function returns
> a VM_FAULT value rather than an errno. Once all instances
> are converted, vm_fault_t will become a distinct type.
>
> see commit 1c8f422059ae ("mm: change return type to vm_fault_t")
> for reference.
>
> Previously vm_insert_mixed returns err which driver
> mapped into VM_FAULT_* type. The new function
> vmf_insert_mixed will replace this inefficiency by
> returning VM_FAULT_* type.

I really think this changelog could do with more work. Specifically for
this patch, I'd just say:

Convert v3d_gem_fault to return vm_fault_t

Instead of converting an errno into a vm_fault_t ourselves, use
vmf_insert_mixed() which returns a vm_fault_t directly.

> unsigned long pfn;
> pgoff_t pgoff;
> - int ret;
>
> /* We don't use vmf->pgoff since that has the fake offset: */
> pgoff = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
> pfn = page_to_pfn(bo->pages[pgoff]);
>
> - ret = vm_insert_mixed(vma, vmf->address, __pfn_to_pfn_t(pfn, PFN_DEV));
> -
> - switch (ret) {
> - case -EAGAIN:
> - case 0:
> - case -ERESTARTSYS:
> - case -EINTR:
> - case -EBUSY:
> - /*
> - * EBUSY is ok: this just means that another thread
> - * already did the job.
> - */
> - return VM_FAULT_NOPAGE;
> - case -ENOMEM:
> - return VM_FAULT_OOM;
> - default:
> - return VM_FAULT_SIGBUS;
> - }
> + return vmf_insert_mixed(vma, vmf->address,
> + __pfn_to_pfn_t(pfn, PFN_DEV));
> }

The line-split here is kind of ugly. I'd do a little more extensive surgery:

- unsigned long pfn;
+ pfn_t pfn;

- pfn = page_to_pfn(bo->pages[pgoff]);
+ pfn = __pfn_to_pfn_t(page_to_pfn(bo->pages[pgoff]), PFN_DEV);

+ return vmf_insert_mixed(vma, vmf->address, pfn);

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