[PATCH] gpu: drm: v3d: use new return type vm_fault_t

[PATCH] gpu: drm: v3d: use new return type vm_fault_t

[Souptick Joarder]

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.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
---
 drivers/gpu/drm/v3d/v3d_bo.c  | 23 +++--------------------
 drivers/gpu/drm/v3d/v3d_drv.h |  3 ++-
 2 files changed, 5 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/v3d/v3d_bo.c b/drivers/gpu/drm/v3d/v3d_bo.c
index 7b1e2a5..f4e8de4 100644
--- a/drivers/gpu/drm/v3d/v3d_bo.c
+++ b/drivers/gpu/drm/v3d/v3d_bo.c
@@ -227,37 +227,20 @@ struct reservation_object *v3d_prime_res_obj(struct drm_gem_object *obj)
 	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
 }
 
-int v3d_gem_fault(struct vm_fault *vmf)
+vm_fault_t v3d_gem_fault(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	struct drm_gem_object *obj = vma->vm_private_data;
 	struct v3d_bo *bo = to_v3d_bo(obj);
 	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));
 }
 
 int v3d_mmap(struct file *filp, struct vm_area_struct *vma)
diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
index a043ac3..09aa634 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.h
+++ b/drivers/gpu/drm/v3d/v3d_drv.h
@@ -2,6 +2,7 @@
 /* Copyright (C) 2015-2018 Broadcom */
 
 #include <linux/reservation.h>
+#include <linux/mm_types.h>
 #include <drm/drmP.h>
 #include <drm/drm_encoder.h>
 #include <drm/drm_gem.h>
@@ -248,7 +249,7 @@ int v3d_mmap_bo_ioctl(struct drm_device *dev, void *data,
 		      struct drm_file *file_priv);
 int v3d_get_bo_offset_ioctl(struct drm_device *dev, void *data,
 			    struct drm_file *file_priv);
-int v3d_gem_fault(struct vm_fault *vmf);
+vm_fault_t v3d_gem_fault(struct vm_fault *vmf);
 int v3d_mmap(struct file *filp, struct vm_area_struct *vma);
 struct reservation_object *v3d_prime_res_obj(struct drm_gem_object *obj);
 int v3d_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);
-- 
1.9.1

Re: [PATCH] gpu: drm: v3d: use new return type vm_fault_t

[Matthew Wilcox]

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);