Re: [PATCH 2/2] drm/i915/vlv_dsi: Control panel and backlight enable GPIOs on BYT

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11-12-2019 01:24, Linus Walleij wrote:
> On Mon, Dec 2, 2019 at 4:49 PM Hans de Goede <hdegoede@redhat.com> wrote:
> 
>> There is only one problem, currently is is not possible to
>> unregister a mapping added with pinctrl_register_mappings
>> and the i915 driver is typically a module which can be unloaded
>> and I believe actually is unloaded as part of the i915 CI.
>>
>> pinctrl_register_mappings copies the passed in mapping, but
>> it is a shallow copy, so it contains pointers to the modules
>> const segment and we do not want to re-add another copy of
>> the mapping when the module loads a second time.
>>
>> Fixing this is easy though, there already is a pinctrl_unregister_map()
>> function, we just need to export it so that the i915 driver can
>> remove the mapping when it is unbound.
>>
>> Linus would exporting this function be ok with you?
> 
> Yep!
> 
>> Linus, question what is the purpose of the "dupping" / shallow
>> copying of the argument passed to pinctrl_register_map ?
> 
> The initial commit contained this comment later removed:
> 
> +       /*
> +        * Make a copy of the map array - string pointers will end up in the
> +        * kernel const section anyway so these do not need to be deep copied.
> +        */
> 
> The use was to free up memory for platforms using boardfiles
> with a gazillion variants and huge pin control tables, so these
> could be marked  __initdata and discarded after boot.
> As the strings would anyway stay around we didn't need to
> deep copy.
> 
> See for example in arch/arm/mach-u300/core.c
> static struct pinctrl_map __initdata u300_pinmux_map[]
> 
>> Since
>> it is shallow the mem for any pointers contained within there need
>> to be kept around by the caller, so why not let the caller keep
>> the pinctrl_map struct itself around too?
> 
> So the strings will be kept around because the kernel can't get
> rid of strings. (Yeah it is silly, should haven been fixed ages
> ago, but not by me, haha :)
> 
>> If we are going to export pinctrl_unregister_map() we need to make it
>> do the right thing for dupped maps too, we can just store the dup flag
>> in struct pinctrl_maps. So this is easy, but I wonder if we cannot
>> get rid of the dupping all together ?
> 
> Maybe ... I don't know. What do you think? I suppose you could
> make u300 crash if you do that.

I've prepared a patch which makes pinctrl_register_mappings remember
if the mapping is dupped or not (store the dup value in struct pinctrl_maps);
and which modifies pinctrl_unregister_map() to do the right thing
depending on the stored dup value.

I still need to test the new series and then I will post it.

Regards,

Hans