linux-kernel - [patch 2/7] drm/vmgfx: Replace kmap

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Date:   Wed, 03 Mar 2021 14:20:25 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     VMware Graphics <linux-graphics-maintainer@...are.com>,
        Roland Scheidegger <sroland@...are.com>,
        Zack Rusin <zackr@...are.com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Christian Koenig <christian.koenig@....com>,
        Huang Rui <ray.huang@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Gerd Hoffmann <kraxel@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        spice-devel@...ts.freedesktop.org, Ben Skeggs <bskeggs@...hat.com>,
        nouveau@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        intel-gfx@...ts.freedesktop.org
Subject: [patch 2/7] drm/vmgfx: Replace kmap_atomic()

From: Thomas Gleixner <tglx@...utronix.de>

There is no reason to disable pagefaults and preemption as a side effect of
kmap_atomic_prot().

Use kmap_local_page_prot() instead and document the reasoning for the
mapping usage with the given pgprot.

Remove the NULL pointer check for the map. These functions return a valid
address for valid pages and the return was bogus anyway as it would have
left preemption and pagefaults disabled.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: VMware Graphics <linux-graphics-maintainer@...are.com>
Cc: Roland Scheidegger <sroland@...are.com>
Cc: Zack Rusin <zackr@...are.com>
Cc: David Airlie <airlied@...ux.ie>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org
---
 drivers/gpu/drm/vmwgfx/vmwgfx_blit.c |   30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

--- a/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c
@@ -375,12 +375,12 @@ static int vmw_bo_cpu_blit_line(struct v
 		copy_size = min_t(u32, copy_size, PAGE_SIZE - src_page_offset);
 
 		if (unmap_src) {
-			kunmap_atomic(d->src_addr);
+			kunmap_local(d->src_addr);
 			d->src_addr = NULL;
 		}
 
 		if (unmap_dst) {
-			kunmap_atomic(d->dst_addr);
+			kunmap_local(d->dst_addr);
 			d->dst_addr = NULL;
 		}
 
@@ -388,12 +388,8 @@ static int vmw_bo_cpu_blit_line(struct v
 			if (WARN_ON_ONCE(dst_page >= d->dst_num_pages))
 				return -EINVAL;
 
-			d->dst_addr =
-				kmap_atomic_prot(d->dst_pages[dst_page],
-						 d->dst_prot);
-			if (!d->dst_addr)
-				return -ENOMEM;
-
+			d->dst_addr = kmap_local_page_prot(d->dst_pages[dst_page],
+							   d->dst_prot);
 			d->mapped_dst = dst_page;
 		}
 
@@ -401,12 +397,8 @@ static int vmw_bo_cpu_blit_line(struct v
 			if (WARN_ON_ONCE(src_page >= d->src_num_pages))
 				return -EINVAL;
 
-			d->src_addr =
-				kmap_atomic_prot(d->src_pages[src_page],
-						 d->src_prot);
-			if (!d->src_addr)
-				return -ENOMEM;
-
+			d->src_addr = kmap_local_page_prot(d->src_pages[src_page],
+							   d->src_prot);
 			d->mapped_src = src_page;
 		}
 		diff->do_cpy(diff, d->dst_addr + dst_page_offset,
@@ -436,8 +428,10 @@ static int vmw_bo_cpu_blit_line(struct v
  *
  * Performs a CPU blit from one buffer object to another avoiding a full
  * bo vmap which may exhaust- or fragment vmalloc space.
- * On supported architectures (x86), we're using kmap_atomic which avoids
- * cross-processor TLB- and cache flushes and may, on non-HIGHMEM systems
+ *
+ * On supported architectures (x86), we're using kmap_local_prot() which
+ * avoids cross-processor TLB- and cache flushes. kmap_local_prot() will
+ * either map a highmem page with the proper pgprot on HIGHMEM=y systems or
  * reference already set-up mappings.
  *
  * Neither of the buffer objects may be placed in PCI memory
@@ -500,9 +494,9 @@ int vmw_bo_cpu_blit(struct ttm_buffer_ob
 	}
 out:
 	if (d.src_addr)
-		kunmap_atomic(d.src_addr);
+		kunmap_local(d.src_addr);
 	if (d.dst_addr)
-		kunmap_atomic(d.dst_addr);
+		kunmap_local(d.dst_addr);
 
 	return ret;
 }