[PATCH linux dev-5.10 06/35] ARM: dts: aspeed: rainier: Add leds that are off PCA9552

[Joel Stanley]

On Fri, 12 Mar 2021 at 07:05, vishwanatha subbanna
<vishwa at linux.vnet.ibm.com> wrote:
>
>
>
> On 12-Mar-2021, at 6:00 AM, Joel Stanley <joel at jms.id.au> wrote:
>
> On Fri, 12 Mar 2021 at 00:21, Milton Miller II <miltonm at us.ibm.com> wrote:
>
>
>
>
> -----"openbmc" <openbmc-bounces+miltonm=us.ibm.com at lists.ozlabs.org> wrote: -----
>
> To: Eddie James <eajames at linux.ibm.com>
> From: Joel Stanley
> Sent by: "openbmc"
> Date: 03/11/2021 06:09PM
> Cc: OpenBMC Maillist <openbmc at lists.ozlabs.org>
> Subject: [EXTERNAL] Re: [PATCH linux dev-5.10 06/35] ARM: dts:
> aspeed: rainier: Add leds that are off PCA9552
>
> On Mon, 8 Mar 2021 at 22:54, Eddie James <eajames at linux.ibm.com>
> wrote:
>
>
> From: Vishwanatha Subbanna <vishwa at linux.vnet.ibm.com>
>
> These LEDs are on the fans and are connected via a
> pca9551 i2c expander
>
>
> This change doesn't make sense. The pca9551 is an i2c LED expander,
> so
> we don't need to expose the pins as GPIOs and then attach a gpio-leds
> driver to them. We should instead simply configure the pca955x driver
> to drive the LEDs as LEDs.
>
>
> I'll refresh your memory on why we have been doing this in our
> devie trees and then let you consider if this is desired or not.
>
> The led system insistes on creating a compact map (no holes) (as
> does the reset subsystem).
>
> However, this means the relative led number for a pin changes
> as the prior pins change from gpio to led configuration.
>
> For example if pins 2 and 7 are leds, they become leds 0 and 1.
> Changing pin 5 to also be an led means that pin 7 is now led 2
> not led 1 on the led subsystem.
>
>
> Thanks for the rationale reminder.
>
> Are these led numbers important to userspace, or does the renumbering
> affect device tree changes only?
>
>
>
> Here are my technical needs.
> - I need these LEDs associated with names and this __must not__ change
> - I need those LEDs represented as `/sys/class/leds/<$name>`
>
> What can I do :
> - use `leds-gpio` like how it’s done today
>
> OR
>
> - Use “label” in PCA955X_TYPE_LED
>    - However, putting this label, it results in `/sys/class/leds/pca955x:<$label>`. As opposed to `/sys/class/leds/<$label>`.
>
> Is there a way where I can get `/sys/class/leds/<$label>` ?. I did not get this from the documentation. Seeing pca955x on 100 entries seems a noise

The prefix has been present in the driver since it was introduced in
2008. Is there any reason we can't have userspace ignore the pca955x
prefix?

Cheers,

Joel