On Mon, 20 Mar 2023, Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx> wrote:
> From: Matt Roper <matthew.d.roper@xxxxxxxxx>
>
> We occasionally see the PCI device in a non-accessible state at the
> point the driver is loaded. When this happens, all BAR accesses will
> read back as 0xFFFFFFFF. Rather than reading registers and
> misinterpreting their (invalid) values, let's specifically check for
> 0xFFFFFFFF in a register that cannot have that value to see if the
> device is accessible.
>
> Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Signed-off-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 34 +++++++++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index e1e1f34490c8e..14ec45e6facfa 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -2602,11 +2602,45 @@ static int uncore_forcewake_init(struct intel_uncore *uncore)
> return 0;
> }
>
> +static int sanity_check_mmio_access(struct intel_uncore *uncore)
> +{
> + struct drm_i915_private *i915 = uncore->i915;
> +
> + if (GRAPHICS_VER(i915) < 8)
> + return 0;
> +
> + /*
> + * Sanitycheck that MMIO access to the device is working properly. If
> + * the CPU is unable to communcate with a PCI device, BAR reads will
> + * return 0xFFFFFFFF. Let's make sure the device isn't in this state
> + * before we start trying to access registers.
> + *
> + * We use the primary GT's forcewake register as our guinea pig since
> + * it's been around since HSW and it's a masked register so the upper
> + * 16 bits can never read back as 1's if device access is operating
> + * properly.
> + *
> + * If MMIO isn't working, we'll wait up to 2 seconds to see if it
> + * recovers, then give up.
> + */
> +#define COND (__raw_uncore_read32(uncore, FORCEWAKE_MT) != ~0)
> + if (wait_for(COND, 2000) == -ETIMEDOUT) {
I guess this somewhat reimplements intel_wait_for_register_fw()?
> + drm_err(&i915->drm, "Device is non-operational; MMIO access returns 0xFFFFFFFF!\n");
> + return -EIO;
> + }
> +
> + return 0;
> +}
> +
> int intel_uncore_init_mmio(struct intel_uncore *uncore)
> {
> struct drm_i915_private *i915 = uncore->i915;
> int ret;
>
> + ret = sanity_check_mmio_access(uncore);
> + if (ret)
> + return ret;
> +
> /*
> * The boot firmware initializes local memory and assesses its health.
> * If memory training fails, the punit will have been instructed to
--
Jani Nikula, Intel Open Source Graphics Center
