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

[Lucas De Marchi]

On Tue, Feb 22, 2022 at 08:22:01PM +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.
>
>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>
>
>Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan at intel.com>
>---
> drivers/gpu/drm/drm_cache.c | 54 +++++++++++++++++++++++++++++++++++++
> include/drm/drm_cache.h     |  3 +++
> 2 files changed, 57 insertions(+)
>
>diff --git a/drivers/gpu/drm/drm_cache.c b/drivers/gpu/drm/drm_cache.c
>index a21c1350eb09..eb0bcd33665e 100644
>--- a/drivers/gpu/drm/drm_cache.c
>+++ b/drivers/gpu/drm/drm_cache.c
>@@ -358,6 +358,54 @@ 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
>+ * @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.

although one could do drm_memcpy_from_wc(IOSYS_MAP_INIT_VADDR(addr), ...

(if IOSYS_MAP_INIT_VADDR provided a cast to the struct).

>+ */
>+void drm_memcpy_from_wc_vaddr(void *dst, const struct iosys_map *src,

name here is confusing as we are copying *to* system memory. Maybe
drm_memcpy_vaddr_from_wc()? Not sure it's better. Maybe someone in Cc
has a better suggestion

( To be honest, this whole _from_wc() suffix sound weird when are checking I/O
   vs system memory.... it may have been the motivation, but maybe it
   shouldn't be the name of the memcpy() variant )

The implementation looks ok and follows drm_memcpy_from_wc()

Lucas De Marchi

>+			      unsigned long len)
>+{
>+	if (WARN_ON(in_interrupt())) {
>+		iosys_map_memcpy_from(dst, src, 0, len);
>+		return;
>+	}
>+
>+	if (static_branch_likely(&has_movntdqa)) {
>+		__drm_memcpy_from_wc(dst,
>+				     src->is_iomem ?
>+				     (void const __force *)src->vaddr_iomem :
>+				     src->vaddr,
>+				     len);
>+		return;
>+	}
>+
>+	iosys_map_memcpy_from(dst, src, 0, 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 +430,12 @@ 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..8f48e4dcd7dc 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,
>+			      unsigned long len);
> #endif
>-- 
>2.25.1
>