Re: [Intel-gfx] [CI 1/4] drm/i915/gt: Explicitly clear BB_OFFSET for new contexts

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 28/03/2022 18:25, Matthew Auld wrote:
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> Even though the initial protocontext we load onto HW has the register
> cleared, by the time we save it into the default image, BB_OFFSET has
> had the enable bit set. Reclear BB_OFFSET for each new context.

Intriguing - is there any impact to this which would require cc: stable?

Regards,

Tvrtko

> Testcase: igt/i915_selftests/gt_lrc
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_engine_regs.h |  1 +
>   drivers/gpu/drm/i915/gt/intel_lrc.c         | 17 +++++++++++++++++
>   drivers/gpu/drm/i915/gt/selftest_lrc.c      |  5 +++++
>   3 files changed, 23 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_regs.h b/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> index 0bf8b45c9319..d6da3bbf66f8 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_regs.h
> @@ -109,6 +109,7 @@
>   #define RING_SBBSTATE(base)			_MMIO((base) + 0x118) /* hsw+ */
>   #define RING_SBBADDR_UDW(base)			_MMIO((base) + 0x11c) /* gen8+ */
>   #define RING_BBADDR(base)			_MMIO((base) + 0x140)
> +#define RING_BB_OFFSET(base)			_MMIO((base) + 0x158)
>   #define RING_BBADDR_UDW(base)			_MMIO((base) + 0x168) /* gen8+ */
>   #define CCID(base)				_MMIO((base) + 0x180)
>   #define   CCID_EN				BIT(0)
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 07bef7128fdb..f673bae97a03 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -662,6 +662,18 @@ static int lrc_ring_mi_mode(const struct intel_engine_cs *engine)
>   		return -1;
>   }
>   
> +static int lrc_ring_bb_offset(const struct intel_engine_cs *engine)
> +{
> +	if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50))
> +		return 0x80;
> +	else if (GRAPHICS_VER(engine->i915) >= 12)
> +		return 0x70;
> +	else if (GRAPHICS_VER(engine->i915) >= 9)
> +		return 0x64;
> +	else
> +		return -1;
> +}
> +
>   static int lrc_ring_gpr0(const struct intel_engine_cs *engine)
>   {
>   	if (GRAPHICS_VER_FULL(engine->i915) >= IP_VER(12, 50))
> @@ -768,6 +780,7 @@ static void init_common_regs(u32 * const regs,
>   			     bool inhibit)
>   {
>   	u32 ctl;
> +	int loc;
>   
>   	ctl = _MASKED_BIT_ENABLE(CTX_CTRL_INHIBIT_SYN_CTX_SWITCH);
>   	ctl |= _MASKED_BIT_DISABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT);
> @@ -779,6 +792,10 @@ static void init_common_regs(u32 * const regs,
>   	regs[CTX_CONTEXT_CONTROL] = ctl;
>   
>   	regs[CTX_TIMESTAMP] = ce->runtime.last;
> +
> +	loc = lrc_ring_bb_offset(engine);
> +	if  (loc != -1)
> +		regs[loc + 1] = 0;
>   }
>   
>   static void init_wa_bb_regs(u32 * const regs,
> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> index 21c29d315cc0..13f57c7c4224 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
> @@ -323,6 +323,11 @@ static int live_lrc_fixed(void *arg)
>   				lrc_ring_cmd_buf_cctl(engine),
>   				"RING_CMD_BUF_CCTL"
>   			},
> +			{
> +				i915_mmio_reg_offset(RING_BB_OFFSET(engine->mmio_base)),
> +				lrc_ring_bb_offset(engine),
> +				"RING_BB_OFFSET"
> +			},
>   			{ },
>   		}, *t;
>   		u32 *hw;