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

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@linux.intel.com Cc: Maxime Ripard mripard@kernel.org Cc: Thomas Zimmermann tzimmermann@suse.de Cc: David Airlie airlied@linux.ie Cc: Daniel Vetter daniel@ffwll.ch Cc: Thomas Hellstr_m thomas.hellstrom@linux.intel.com

Signed-off-by: Balasubramani Vivekanandan balasubramani.vivekanandan@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