Reading out of write-combining mapped memory is typically very slow since the CPU doesn't prefetch. However some archs have special instructions to do this.
So add a best-effort memcpy_from_wc taking dma-buf-map pointer arguments that attempts to use a fast prefetching memcpy and otherwise falls back to ordinary memcopies, taking the iomem tagging into account.
The code is largely copied from i915_memcpy_from_wc.
Cc: Daniel Vetter daniel@ffwll.ch Cc: Christian König christian.koenig@amd.com Suggested-by: Daniel Vetter daniel@ffwll.ch Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com Acked-by: Christian König christian.koenig@amd.com Acked-by: Daniel Vetter daniel@ffwll.ch --- v7: - Perform a memcpy even if warning with in_interrupt(). Suggested by Christian König. - Fix compilation failure on !X86 (Reported by kernel test robot lkp@intel.com) v8: - Skip kerneldoc for drm_memcpy_init_early() - Export drm_memcpy_from_wc() also for non-x86. --- Documentation/gpu/drm-mm.rst | 2 +- drivers/gpu/drm/drm_cache.c | 148 +++++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_drv.c | 2 + include/drm/drm_cache.h | 7 ++ 4 files changed, 158 insertions(+), 1 deletion(-)
diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index 21be6deadc12..c66058c5bce7 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -469,7 +469,7 @@ DRM MM Range Allocator Function References .. kernel-doc:: drivers/gpu/drm/drm_mm.c :export:
-DRM Cache Handling +DRM Cache Handling and Fast WC memcpy() ==================
.. kernel-doc:: drivers/gpu/drm/drm_cache.c diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c index 79a50ef1250f..546599f19a93 100644 --- a/drivers/gpu/drm/drm_cache.c +++ b/drivers/gpu/drm/drm_cache.c @@ -28,6 +28,7 @@ * Authors: Thomas Hellström <thomas-at-tungstengraphics-dot-com> */
+#include <linux/dma-buf-map.h> #include <linux/export.h> #include <linux/highmem.h> #include <linux/mem_encrypt.h> @@ -35,6 +36,9 @@
#include <drm/drm_cache.h>
+/* A small bounce buffer that fits on the stack. */ +#define MEMCPY_BOUNCE_SIZE 128 + #if defined(CONFIG_X86) #include <asm/smp.h>
@@ -209,3 +213,147 @@ bool drm_need_swiotlb(int dma_bits) return max_iomem > ((u64)1 << dma_bits); } EXPORT_SYMBOL(drm_need_swiotlb); + +static void memcpy_fallback(struct dma_buf_map *dst, + const struct dma_buf_map *src, + unsigned long len) +{ + if (!dst->is_iomem && !src->is_iomem) { + memcpy(dst->vaddr, src->vaddr, len); + } else if (!src->is_iomem) { + dma_buf_map_memcpy_to(dst, src->vaddr, len); + } else if (!dst->is_iomem) { + memcpy_fromio(dst->vaddr, src->vaddr_iomem, len); + } else { + /* + * Bounce size is not performance tuned, but using a + * bounce buffer like this is significantly faster than + * resorting to ioreadxx() + iowritexx(). + */ + char bounce[MEMCPY_BOUNCE_SIZE]; + void __iomem *_src = src->vaddr_iomem; + void __iomem *_dst = dst->vaddr_iomem; + + while (len >= MEMCPY_BOUNCE_SIZE) { + memcpy_fromio(bounce, _src, MEMCPY_BOUNCE_SIZE); + memcpy_toio(_dst, bounce, MEMCPY_BOUNCE_SIZE); + _src += MEMCPY_BOUNCE_SIZE; + _dst += MEMCPY_BOUNCE_SIZE; + len -= MEMCPY_BOUNCE_SIZE; + } + if (len) { + memcpy_fromio(bounce, _src, MEMCPY_BOUNCE_SIZE); + memcpy_toio(_dst, bounce, MEMCPY_BOUNCE_SIZE); + } + } +} + +#ifdef CONFIG_X86 + +static DEFINE_STATIC_KEY_FALSE(has_movntdqa); + +static void __memcpy_ntdqa(void *dst, const void *src, unsigned long len) +{ + kernel_fpu_begin(); + + while (len >= 4) { + asm("movntdqa (%0), %%xmm0\n" + "movntdqa 16(%0), %%xmm1\n" + "movntdqa 32(%0), %%xmm2\n" + "movntdqa 48(%0), %%xmm3\n" + "movaps %%xmm0, (%1)\n" + "movaps %%xmm1, 16(%1)\n" + "movaps %%xmm2, 32(%1)\n" + "movaps %%xmm3, 48(%1)\n" + :: "r" (src), "r" (dst) : "memory"); + src += 64; + dst += 64; + len -= 4; + } + while (len--) { + asm("movntdqa (%0), %%xmm0\n" + "movaps %%xmm0, (%1)\n" + :: "r" (src), "r" (dst) : "memory"); + src += 16; + dst += 16; + } + + kernel_fpu_end(); +} + +/* + * __drm_memcpy_from_wc copies @len bytes from @src to @dst using + * non-temporal instructions where available. Note that all arguments + * (@src, @dst) must be aligned to 16 bytes and @len must be a multiple + * of 16. + */ +static void __drm_memcpy_from_wc(void *dst, const void *src, unsigned long len) +{ + if (unlikely(((unsigned long)dst | (unsigned long)src | len) & 15)) + memcpy(dst, src, len); + else if (likely(len)) + __memcpy_ntdqa(dst, src, len >> 4); +} + +/** + * drm_memcpy_from_wc - Perform the fastest available memcpy from a source + * that may be WC. + * @dst: The destination pointer + * @src: The source pointer + * @len: The size of the area o transfer in bytes + * + * Tries an arch optimized memcpy for prefetching reading out of a WC region, + * and if no such beast is available, falls back to a normal memcpy. + */ +void drm_memcpy_from_wc(struct dma_buf_map *dst, + const struct dma_buf_map *src, + unsigned long len) +{ + if (WARN_ON(in_interrupt())) { + memcpy_fallback(dst, src, len); + return; + } + + if (static_branch_likely(&has_movntdqa)) { + __drm_memcpy_from_wc(dst->is_iomem ? + (void __force *)dst->vaddr_iomem : + dst->vaddr, + src->is_iomem ? + (void const __force *)src->vaddr_iomem : + src->vaddr, + len); + return; + } + + memcpy_fallback(dst, src, len); +} +EXPORT_SYMBOL(drm_memcpy_from_wc); + +/* + * drm_memcpy_init_early - One time initialization of the WC memcpy code + */ +void drm_memcpy_init_early(void) +{ + /* + * Some hypervisors (e.g. KVM) don't support VEX-prefix instructions + * emulation. So don't enable movntdqa in hypervisor guest. + */ + if (static_cpu_has(X86_FEATURE_XMM4_1) && + !boot_cpu_has(X86_FEATURE_HYPERVISOR)) + static_branch_enable(&has_movntdqa); +} +#else +void drm_memcpy_from_wc(struct dma_buf_map *dst, + const struct dma_buf_map *src, + unsigned long len) +{ + WARN_ON(in_interrupt()); + + memcpy_fallback(dst, src, len); +} +EXPORT_SYMBOL(drm_memcpy_from_wc); + +void drm_memcpy_init_early(void) +{ +} +#endif /* CONFIG_X86 */ diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index 3d8d68a98b95..8804ec7d3215 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -35,6 +35,7 @@ #include <linux/slab.h> #include <linux/srcu.h>
+#include <drm/drm_cache.h> #include <drm/drm_client.h> #include <drm/drm_color_mgmt.h> #include <drm/drm_drv.h> @@ -1041,6 +1042,7 @@ static int __init drm_core_init(void)
drm_connector_ida_init(); idr_init(&drm_minors_idr); + drm_memcpy_init_early();
ret = drm_sysfs_init(); if (ret < 0) { diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h index e9ad4863d915..cc9de1632dd3 100644 --- a/include/drm/drm_cache.h +++ b/include/drm/drm_cache.h @@ -35,6 +35,8 @@
#include <linux/scatterlist.h>
+struct dma_buf_map; + void drm_clflush_pages(struct page *pages[], unsigned long num_pages); void drm_clflush_sg(struct sg_table *st); void drm_clflush_virt_range(void *addr, unsigned long length); @@ -70,4 +72,9 @@ static inline bool drm_arch_can_wc_memory(void) #endif }
+void drm_memcpy_init_early(void); + +void drm_memcpy_from_wc(struct dma_buf_map *dst, + const struct dma_buf_map *src, + unsigned long len); #endif