Re: [Intel-gfx] [PATCH] drm/i915/gt: prevent forcewake releases during BAR resize

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Mar 08, 2023 at 12:23:49PM +0100, Andrzej Hajda wrote:
> Tests on DG2 machines show that releasing forcewakes during BAR resize
> results later in forcewake ack timeouts. Since forcewakes can be realeased
> asynchronously the simplest way to prevent it is to get all forcewakes
> for duration of BAR resizing.
> 
> Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_region_lmem.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_region_lmem.c b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> index 89fdfc67f8d1e0..5a01dc6ca08324 100644
> --- a/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> +++ b/drivers/gpu/drm/i915/gt/intel_region_lmem.c
> @@ -54,6 +54,7 @@ static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t
>  	struct resource *root_res;
>  	resource_size_t rebar_size;
>  	resource_size_t current_size;
> +	intel_wakeref_t wakeref;
>  	u32 pci_cmd;
>  	int i;
>  
> @@ -102,6 +103,14 @@ static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t
>  		return;
>  	}
>  
> +	/*
> +	 * Releasing forcewake during BAR resizing results in later forcewake
> +	 * ack timeouts and former can happen any time - it is asynchronous.
> +	 * Grabbing all forcewakes prevents it.
> +	 */
> +	with_intel_runtime_pm(i915->uncore.rpm, wakeref)

I believe that instead of the with_rpm you should probably get the rpm ref here
and return after returning the forcewake put. So you also ensure that we are
not going to suspend and allowing D3 during the resize.

> +		intel_uncore_forcewake_get(&i915->uncore, FORCEWAKE_ALL);
> +
>  	/* First disable PCI memory decoding references */
>  	pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
>  	pci_write_config_dword(pdev, PCI_COMMAND,
> @@ -111,6 +120,9 @@ static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t
>  
>  	pci_assign_unassigned_bus_resources(pdev->bus);
>  	pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
> +
> +	with_intel_runtime_pm(i915->uncore.rpm, wakeref)
> +		intel_uncore_forcewake_put(&i915->uncore, FORCEWAKE_ALL);
>  }
>  #else
>  static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t lmem_size) {}
> -- 
> 2.34.1
>