Re: [PATCH 7/8] drm/i915: Add support to parse DMI table and get platform memory info (v3)

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Mar 07, 2016 at 05:05:45PM -0800, Matt Roper wrote:
> From: Shobhit Kumar <shobhit.kumar@intel.com>
> 
> This is needed for WM computation workaround for arbitrated display
> bandwidth.
> 
> v2: Address Matt's review comments
>     - Be more paranoid while dmi decoding
>     - Also add support for decoding speed from configured memory speed
>       if availble in DMI memory entry
> 
> v3 (by Matt):
>  - Use memdev_dmi_entry from dmi.h
>  - Don't try to use/compare negative numbers in unsigned types
> 
> Cc: matthew.d.roper@intel.com
> Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 34 ++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_drv.h |  7 +++++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 4aa3db6..4259afe 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -49,6 +49,7 @@
>  #include <linux/pm.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/oom.h>
> +#include <linux/dmi.h>
>  
>  
>  static int i915_getparam(struct drm_device *dev, void *data,
> @@ -973,6 +974,33 @@ static void i915_mmio_cleanup(struct drm_device *dev)
>  	pci_iounmap(dev->pdev, dev_priv->regs);
>  }
>  
> +static void dmi_decode_memory_info(const struct dmi_header *hdr, void *priv)
> +{
> +	struct drm_i915_private *dev_priv = (struct drm_i915_private *) priv;
> +	const struct memdev_dmi_entry *memdev =
> +		(const struct memdev_dmi_entry *)hdr;
> +	uint16_t mem_speed = 0;
> +
> +	if (hdr->type != DMI_ENTRY_MEM_DEVICE)
> +		return;
> +
> +	/* Get the speed */
> +	if (hdr->length > offsetof(struct memdev_dmi_entry, conf_mem_clk_speed))
> +		mem_speed = memdev->conf_mem_clk_speed;
> +	else if (hdr->length > offsetof(struct memdev_dmi_entry, speed))
> +		mem_speed = memdev->speed;
> +	else
> +		return;
> +
> +	dev_priv->dmi.mem_channel++;
> +
> +	/* All channels are expected to have same the speed */
> +	if (dev_priv->dmi.mem_speed == 0)
> +		dev_priv->dmi.mem_speed = mem_speed;
> +	else if (mem_speed != dev_priv->dmi.mem_speed)
> +		dev_priv->dmi.valid = false;
> +}

Dunno if this was covered already, but trusting DMI for this feels
rather fragile to me. Isn't there some way to get the relevant
information from the hardware itself?

> +
>  /**
>   * i915_driver_load - setup chip and create an initial config
>   * @dev: DRM device
> @@ -1000,6 +1028,12 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
>  	dev->dev_private = dev_priv;
>  	dev_priv->dev = dev;
>  
> +	/* walk the dmi device table for getting platform memory information */
> +	dev_priv->dmi.valid = true;
> +	dmi_walk(dmi_decode_memory_info, dev_priv);
> +	if (!dev_priv->dmi.mem_speed)
> +		dev_priv->dmi.valid = false;
> +
>  	/* Setup the write-once "constant" device info */
>  	device_info = (struct intel_device_info *)&dev_priv->info;
>  	memcpy(device_info, info, sizeof(dev_priv->info));
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index f37ac12..a2a7d8d 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2022,6 +2022,13 @@ struct drm_i915_private {
>  	 * NOTE: This is the dri1/ums dungeon, don't add stuff here. Your patch
>  	 * will be rejected. Instead look for a better place.
>  	 */
> +
> +	/* DMI data for memory bandwidth calculation */
> +	struct {
> +		bool valid;
> +		uint16_t mem_channel;
> +		int16_t mem_speed;
> +	} dmi;
>  };
>  
>  static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
> -- 
> 2.1.4
> 
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-- 
Ville Syrjälä
Intel OTC
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