linux-kernel - [PATCH V9 04/24] LoongArch: Add writecombine support for drm

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Date:   Sat, 30 Apr 2022 17:04:58 +0800
From:   Huacai Chen <chenhuacai@...ngson.cn>
To:     Arnd Bergmann <arnd@...db.de>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH V9 04/24] LoongArch: Add writecombine support for drm

LoongArch maintains cache coherency in hardware, but its WUC attribute
(Weak-ordered UnCached, which is similar to WC) is out of the scope of
cache coherency machanism. This means WUC can only used for write-only
memory regions.

Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 drivers/gpu/drm/drm_vm.c         | 2 +-
 drivers/gpu/drm/ttm/ttm_module.c | 2 +-
 include/drm/drm_cache.h          | 8 ++++++++
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_vm.c b/drivers/gpu/drm/drm_vm.c
index e957d4851dc0..f024dc93939e 100644
--- a/drivers/gpu/drm/drm_vm.c
+++ b/drivers/gpu/drm/drm_vm.c
@@ -69,7 +69,7 @@ static pgprot_t drm_io_prot(struct drm_local_map *map,
 	pgprot_t tmp = vm_get_page_prot(vma->vm_flags);
 
 #if defined(__i386__) || defined(__x86_64__) || defined(__powerpc__) || \
-    defined(__mips__)
+    defined(__mips__) || defined(__loongarch__)
 	if (map->type == _DRM_REGISTERS && !(map->flags & _DRM_WRITE_COMBINING))
 		tmp = pgprot_noncached(tmp);
 	else
diff --git a/drivers/gpu/drm/ttm/ttm_module.c b/drivers/gpu/drm/ttm/ttm_module.c
index a3ad7c9736ec..b3fffe7b5062 100644
--- a/drivers/gpu/drm/ttm/ttm_module.c
+++ b/drivers/gpu/drm/ttm/ttm_module.c
@@ -74,7 +74,7 @@ pgprot_t ttm_prot_from_caching(enum ttm_caching caching, pgprot_t tmp)
 #endif /* CONFIG_UML */
 #endif /* __i386__ || __x86_64__ */
 #if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
-	defined(__powerpc__) || defined(__mips__)
+	defined(__powerpc__) || defined(__mips__) || defined(__loongarch__)
 	if (caching == ttm_write_combined)
 		tmp = pgprot_writecombine(tmp);
 	else
diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h
index 22deb216b59c..08e0e3ffad13 100644
--- a/include/drm/drm_cache.h
+++ b/include/drm/drm_cache.h
@@ -67,6 +67,14 @@ static inline bool drm_arch_can_wc_memory(void)
 	 * optimization entirely for ARM and arm64.
 	 */
 	return false;
+#elif defined(CONFIG_LOONGARCH)
+	/*
+	 * LoongArch maintains cache coherency in hardware, but its WUC attribute
+	 * (Weak-ordered UnCached, which is similar to WC) is out of the scope of
+	 * cache coherency machanism. This means WUC can only used for write-only
+	 * memory regions.
+	 */
+	return false;
 #else
 	return true;
 #endif
-- 
2.27.0