[PATCH v4 06/15] mei: pxp: support matching with a gfx discrete card

[Greg Kroah-Hartman]

On Thu, Sep 08, 2022 at 05:16:03PM -0700, Daniele Ceraolo Spurio wrote:
> From: Tomas Winkler <tomas.winkler at intel.com>
> 
> With on-boards graphics card, both i915 and MEI
> are in the same device hierarchy with the same parent,
> while for discrete gfx card the MEI is its child device.
> Adjust the match function for that scenario
> by matching MEI parent device with i915.
> 
> V2:
>  1. More detailed commit message
>  2. Check for dev is not null before it is accessed.
> 
> Signed-off-by: Tomas Winkler <tomas.winkler at intel.com>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> Cc: Vitaly Lubart <vitaly.lubart at intel.com>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Reviewed-by: Alan Previn <alan.previn.teres.alexis at intel.com>
> ---
>  drivers/misc/mei/pxp/mei_pxp.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/misc/mei/pxp/mei_pxp.c b/drivers/misc/mei/pxp/mei_pxp.c
> index 17c5d201603f..afc047627800 100644
> --- a/drivers/misc/mei/pxp/mei_pxp.c
> +++ b/drivers/misc/mei/pxp/mei_pxp.c
> @@ -159,17 +159,24 @@ static int mei_pxp_component_match(struct device *dev, int subcomponent,
>  {
>  	struct device *base = data;
>  
> +	if (!dev)
> +		return 0;

How can that happen?

> +
>  	if (!dev->driver || strcmp(dev->driver->name, "i915") ||

That's crazy to assume, but whatever :(

>  	    subcomponent != I915_COMPONENT_PXP)
>  		return 0;
>  
>  	base = base->parent;
> -	if (!base)
> +	if (!base) /* mei device */

Why does this mean that?

Where is that documented?

>  		return 0;
>  
> -	base = base->parent;
> -	dev = dev->parent;
> +	base = base->parent; /* pci device */

Again, why is this the case?

> +	/* for dgfx */
> +	if (base && dev == base)
> +		return 1;
>  
> +	/* for pch */
> +	dev = dev->parent;

You are digging through a random device tree and assuming that you
"know" what the topology is going to be, that feels very very fragile
and ripe for problems going forward.

How do you ensure that this really is they way the tree is for ALL
systems?

thanks,

greg k-h