[Intel-gfx] [PATCH v3 2/7] drm: Add drm_memcpy_from_wc() variant which accepts destination address

[Lucas De Marchi]

On Tue, Apr 26, 2022 at 10:21:43PM +0530, Balasubramani Vivekanandan wrote:
>Fast copy using non-temporal instructions for x86 currently exists at two
>locations. One is implemented in i915 driver at i915/i915_memcpy.c and
>another copy at drm_cache.c. The plan is to remove the duplicate
>implementation in i915 driver and use the functions from drm_cache.c.
>
>A variant of drm_memcpy_from_wc() is added in drm_cache.c which accepts
>address as argument instead of iosys_map for destination. It is a very
>common scenario in i915 to copy from a WC memory type, which may be an
>io memory or a system memory to a destination address pointing to system
>memory. To avoid the overhead of creating iosys_map type for the
>destination, new variant is created to accept the address directly.
>
>Also a new function is exported in drm_cache.c to find if the fast copy
>is supported by the platform or not. It is required for i915.
>
>v2: Added a new argument to drm_memcpy_from_wc_vaddr() which provides
>the offset into the src address to start copy from.
>
>Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>Cc: Maxime Ripard <mripard at kernel.org>
>Cc: Thomas Zimmermann <tzimmermann at suse.de>
>Cc: David Airlie <airlied at linux.ie>
>Cc: Daniel Vetter <daniel at ffwll.ch>
>Cc: Thomas Hellstr_m <thomas.hellstrom at linux.intel.com>

		   ^ utf-8 error?

>
>Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan at intel.com>
>Reviewed-by: Lucas De Marchi <lucas.demarchi at intel.com>
>Reviewed-by: Nirmoy Das <nirmoy.das at intel.com>
>---
> drivers/gpu/drm/drm_cache.c | 55 +++++++++++++++++++++++++++++++++++++
> include/drm/drm_cache.h     |  3 ++
> 2 files changed, 58 insertions(+)
>
>diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
>index 2e2545df3310..8c7af755f7bc 100644
>--- a/drivers/gpu/drm/drm_cache.c
>+++ b/drivers/gpu/drm/drm_cache.c
>@@ -358,6 +358,55 @@ void drm_memcpy_from_wc(struct iosys_map *dst,
> }
> EXPORT_SYMBOL(drm_memcpy_from_wc);
>
>+/**
>+ * drm_memcpy_from_wc_vaddr - Perform the fastest available memcpy from a source
>+ * that may be WC to a destination in system memory.
>+ * @dst: The destination pointer
>+ * @src: The source pointer
>+ * @src_offset: The offset from which to copy
>+ * @len: The size of the area to transfer in bytes
>+ *
>+ * Same as drm_memcpy_from_wc except destination is accepted as system memory
>+ * address. Useful in situations where passing destination address as iosys_map
>+ * is simply an overhead and can be avoided.
>+ */
>+void drm_memcpy_from_wc_vaddr(void *dst, const struct iosys_map *src,
>+			      size_t src_offset, unsigned long len)
>+{
>+	const void *src_addr = src->is_iomem ?
>+				(void const __force *)src->vaddr_iomem :
>+				src->vaddr;

checking this again... this is a layer violation. We do have some in
the codebase, but it'd be good not to add more.

later I'd like these memcpy variants to be moved iosys-map. I'm not sure
if Thomas Zimmermann or Christian agree. Cc'ing them here.

Maybe we could scan the codebase and add a function in iosys-map like:

	void *iosys_map_get_ptr(struct iosys_map *map, bool is_lmem)

... which is similar to the ttm_kmap_obj_virtual() function we have in
ttm.

so the cases where the layer is violated at least they come from a
single function call in iosys_map API rather than directly accessing
is_iomem/vaddr_iomem/vaddr. Thomas/Christian, any opinion here?

Lucas De Marchi

>+
>+	if (WARN_ON(in_interrupt())) {
>+		iosys_map_memcpy_from(dst, src, src_offset, len);
>+		return;
>+	}
>+
>+	if (static_branch_likely(&has_movntdqa)) {
>+		__drm_memcpy_from_wc(dst, src_addr + src_offset, len);
>+		return;
>+	}
>+
>+	iosys_map_memcpy_from(dst, src, src_offset, len);
>+}
>+EXPORT_SYMBOL(drm_memcpy_from_wc_vaddr);
>+
>+/*
>+ * drm_memcpy_fastcopy_supported - Returns if fast copy using non-temporal
>+ * instructions is supported
>+ *
>+ * Returns true if platform has support for fast copying from wc memory type
>+ * using non-temporal instructions. Else false.
>+ */
>+bool drm_memcpy_fastcopy_supported(void)
>+{
>+	if (static_branch_likely(&has_movntdqa))
>+		return true;
>+
>+	return false;
>+}
>+EXPORT_SYMBOL(drm_memcpy_fastcopy_supported);
>+
> /*
>  * drm_memcpy_init_early - One time initialization of the WC memcpy code
>  */
>@@ -382,6 +431,12 @@ void drm_memcpy_from_wc(struct iosys_map *dst,
> }
> EXPORT_SYMBOL(drm_memcpy_from_wc);
>
>+bool drm_memcpy_fastcopy_supported(void)
>+{
>+	return false;
>+}
>+EXPORT_SYMBOL(drm_memcpy_fastcopy_supported);
>+
> void drm_memcpy_init_early(void)
> {
> }
>diff --git a/include/drm/drm_cache.h b/include/drm/drm_cache.h
>index 22deb216b59c..d1b57c84a659 100644
>--- a/include/drm/drm_cache.h
>+++ b/include/drm/drm_cache.h
>@@ -77,4 +77,7 @@ void drm_memcpy_init_early(void);
> void drm_memcpy_from_wc(struct iosys_map *dst,
> 			const struct iosys_map *src,
> 			unsigned long len);
>+bool drm_memcpy_fastcopy_supported(void);
>+void drm_memcpy_from_wc_vaddr(void *dst, const struct iosys_map *src,
>+			      size_t src_offset, unsigned long len);
> #endif
>-- 
>2.25.1
>