Re: [PATCH] drm/i915: Update WaFlushCoherentL3CacheLinesAtContextSwitch

Chris Wilson
2015-07-03T15:42:31Z

On Fri, Jul 03, 2015 at 02:27:31PM +0100, Arun Siluvery wrote:
> In this WA we need to set GEN8_L3SQCREG4[21:21] and reset it after PIPE_CONTROL
> instruction but there is a slight complication as this is applied in WA batch
> where the values are only initialized once.
> Dave identified an issue with the current implementation where the register value
> is read once at the beginning and it is reused; this patch corrects this by saving
> the register value to memory, update register with the bit of our interest and
> restore it back with original value.
>
> This implementation uses MI_LOAD_REGISTER_MEM which is currently only used
> by command parser and was using a default length of 0. This is now updated
> with correct length and moved to appropriate place.
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Dave Gordon <david.s.gordon@intel.com>
> Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> ---
> drivers/gpu/drm/i915/i915_cmd_parser.c | 6 +--
> drivers/gpu/drm/i915/i915_reg.h | 3 +-
> drivers/gpu/drm/i915/intel_lrc.c | 72 +++++++++++++++++++++++++---------
> 3 files changed, 58 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index 306d9e4..430571b 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -131,7 +131,7 @@ static const struct drm_i915_cmd_descriptor common_cmds[] = {
> .mask = MI_GLOBAL_GTT,
> .expected = 0,
> }}, ),
> - CMD( MI_LOAD_REGISTER_MEM, SMI, !F, 0xFF, W | B,
> + CMD( MI_LOAD_REGISTER_MEM(1), SMI, !F, 0xFF, W | B,
> .reg = { .offset = 1, .mask = 0x007FFFFC },
> .bits = {{
> .offset = 0,
> @@ -1021,7 +1021,7 @@ static bool check_cmd(const struct intel_engine_cs *ring,
> * only MI_LOAD_REGISTER_IMM commands.
> */
> if (reg_addr == OACONTROL) {
> - if (desc->cmd.value == MI_LOAD_REGISTER_MEM) {
> + if (desc->cmd.value == MI_LOAD_REGISTER_MEM(1)) {

I had a double take here, but it all comes out in the wash. For one
moment, I thought the cmd matching had changed, but that has the length
masked out.

Reviewed-by: Chris Wilson <chris@cris-wilson.co.uk>

Who will start to complain about all the extra frequent register writes,
probably into common power wells....
-Chris

--
Chris Wilson, Intel Open Source Technology Centre