Re: Leds-gpio discarding the entries in /sys/class/leds : Linux 5.4.38

[Jacek Anaszewski <jacek.anaszewski@gmail.com>]

On 6/22/20 1:07 PM, Vishwanatha Subbanna wrote:
> Hi Jacek,
> 
>> On 22-Jun-2020, at 4:24 PM, Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote:
>>
>> Hi Vishwanatha,
>>
>> On 6/22/20 8:58 AM, Vishwanatha Subbanna wrote:
>>> Thank you very much Jacek.
>>>> On 22-Jun-2020, at 3:12 AM, Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote:
>>>>
>>>> Hi Vishwanatha,
>>>>
>>>> On 6/20/20 7:25 PM, Vishwanatha Subbanna wrote:
>>>>> Hi Jacek,
>>>>> Thank you very much for the quick response. Greatly appreciate that.
>>>>
>>>> You're welcome.
>>>>
>>>>>> On 20-Jun-2020, at 3:27 AM, Jacek Anaszewski <jacek.anaszewski@gmail.com> wrote:
>>>>>>
>>>>>> Hi Vishwanatha,
>>>>>>
>>>>>> Please refer to Documentation/devicetree/bindings/leds/leds-pca955x.txt.
>>>>>>
>>>>>> At first glance I don't get why you have gpio-leds node, which is for
>>>>>> leds-gpio driver.
>>>>> Not sure I understood it right.. But if you are asking me why I have "leds {"  and “gpio-leds” in there, then it is to get the entries in /sys/class/leds.
>>>>> The GPIOs from PCA9552 are connected to LED. Also, that is how we have had in the past, and that worked.
>>>>> Example: https://github.com/openbmc/linux/blob/dev-5.4/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts#L115
>>>>
>>>> Thanks. Yeah, that looks OK, I had to take closer look at the driver.
>>>>
>>>>> The problem I am running into is for : https://github.com/openbmc/linux/blob/dev-5.4/arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts
>>>>>>
>>>>>> On 6/19/20 3:34 PM, Vishwanatha Subbanna wrote:
>>>>>>> Hello,
>>>>>>> I am Vishwanath, working with IBM and looking for your help on one of the issues that I am running into. Would really appreciate help on this. I run Linux 5.4.38
>>>>>>> I have 2 number of PCA9552 chips, one on the Planar and other on the card that is optionally pluggable. The optional card must be plugged prior to booting and is not hot pluggable. In my experiment, I am running *without* the optional card plugged in.
>>>>>>> In the device tree, I have a "leds {" section that looks like below for the PCA9552 that is on the planar and everything works fine and I can see /sys/class/leds/fan0
>>>>>>>   leds {
>>>>>>>          compatible = "gpio-leds”;
>>>>>>>          fan0 {
>>>>>>>              retain-state-shutdown;
>>>>>>>              default-state = "keep";
>>>>>>>              gpios = <&pca0 0 GPIO_ACTIVE_LOW>;
>>>>>>>          };
>>>>>>> };
>>>>>>> &i2c7 {
>>>>>>>      status = "okay”;
>>>>>>>      pca0: pca9552@61 {
>>>>>>>         compatible = "nxp,pca9552";
>>>>>>>          reg = <0x61>;
>>>>>>>          #address-cells = <1>;
>>>>>>>          #size-cells = <0>;
>>>>>>>          gpio-controller;
>>>>>>>          #gpio-cells = <2>;
>>>>>>>          gpio@0 {
>>>>>>>              reg = <0>;
>>>>>>>              type = <PCA955X_TYPE_GPIO>;
>>>>>>>       	};
>>>>>>>      };
>>>>>>> };
>>>>>>> Similarly, if I update the device tree entry for PCA9552 for the card that is optionally pluggable, then I don’t see any leds entries in /sys/class/leds.
>>>>>>
>>>>>> Please share your DT node after the update.
>>>>>>
>>>>> Pasting the GPIO_0 entry only here for brevity.
>>>>> leds {
>>>>>          compatible = "gpio-leds”;
>>>>>          fan0 {
>>>>>              retain-state-shutdown;
>>>>>              default-state = "keep";
>>>>>              gpios = <&pca0 0 GPIO_ACTIVE_LOW>;
>>>>>          };
>>>>>          nvmeslot0 {
>>>>>              retain-state-shutdown;
>>>>>              default-state = "keep";
>>>>>              gpios = <&pca1 0 GPIO_ACTIVE_LOW>;
>>>>>          };
>>>>> };
>>>>> &i2c7 {
>>>>>      status = "okay”;
>>>>>      pca0: pca9552@61 {
>>>>>         compatible = "nxp,pca9552";
>>>>>          reg = <0x61>;
>>>>>          #address-cells = <1>;
>>>>>          #size-cells = <0>;
>>>>>          gpio-controller;
>>>>>          #gpio-cells = <2>;
>>>>>          gpio@0 {
>>>>>              reg = <0>;
>>>>>              type = <PCA955X_TYPE_GPIO>;
>>>>>       	};
>>>>>      };
>>>>> };
>>>>> &i2c13
>>>>> {
>>>>>      pca1: pca9552@60 {
>>>>>         compatible = "nxp,pca9552";
>>>>>         reg = <0x60>;
>>>>>         #address-cells = <1>;
>>>>>         #size-cells = <0>;
>>>>>         gpio-controller;
>>>>>         #gpio-cells = <2>;
>>>>>         gpio@0 {
>>>>>             reg = <0>;
>>>>>             type = <PCA955X_TYPE_GPIO>;
>>>>>         };
>>>>>      };
>>>>> };
>>>>> Thanks
>>>>> !! Vishwa !!
>>>>>>> I don’t even see “fan0” that is on the PCA9552 on planar also. I was expecting that I should see “/sys/class/leds/fan0”.
>>>>>>> However, I could see all the entries in “/proc/device-tree/leds”.
>>>>>>> Data from the failure.
>>>>>>> [    7.895757] leds-pca955x 7-0061: leds-pca955x: Using pca9552 16-bit LED driver at slave address 0x61
>>>>>>> [    7.907659] leds-pca955x 7-0061: gpios 168...183
>>>>
>>>> It is weird that you don't see "fan0" LED since this gpio seems to have
>>>> been properly registered according to this log.
>>>>
>>> This is exactly what I don’t understand. I would expect “fan0” to appear in /sys/class/leds. Is there any reason why this might not be appearing ?..
>>
>> OK, now the reason is clear to me. If leds-gpio driver fails to register
>> any of the LEDs found in DT node it returns with an error from the
>> probe(), which results in unregistering any of the LEDs registered in
>> the previous iteration steps.
>>
>> Look at the function gpio_leds_create() in
>> drivers/leds/leds-gpio.c.
>>
>> Probably it is devm_fwnode_get_gpiod_from_child() that fails
>> while parsing nvmeslot0 node.
> 
> Is this how it is designed or a bug ?.. From a system standpoint, not having an optional card results in not seeing the ones that are present on the system.
> Would you think it is worthwhile to modify to not chuck off what is existing because something optional is not plugged in ?.. I believe the I2C driver handles this scenario by putting an error message but still consumes what is present.

Well, this code is in mainline for some time and we cannot guarantee
the someone does not rely on this behavior.

You mentioned, that your card is not hot-pluggable so it is even more
justified to treat the two hardware setups as demanding a separate DT.

Otherwise you could probably employ DT overlays mechanism.

-- 
Best regards,
Jacek Anaszewski