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Date:   Mon, 9 Oct 2023 10:46:28 -0700
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Subject: Re: [RFT PATCH 14/21] hte: tegra194: don't access struct gpio_chip
Content-Language: en-US
From:   Dipen Patel <dipenp@nvidia.com>
To:     Bartosz Golaszewski <brgl@bgdev.pl>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Janusz Krzysztofik <jmkrzyszt@gmail.com>,
        Tony Lindgren <tony@atomide.com>,
        Russell King <linux@armlinux.org.uk>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Hans de Goede <hdegoede@redhat.com>,
        Mark Gross <markgross@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org,
        linux-acpi@vger.kernel.org, timestamp@lists.linux.dev,
        linux-tegra@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
References: <20230905185309.131295-1-brgl@bgdev.pl>
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On 10/9/23 9:34 AM, Dipen Patel wrote:
> On 10/8/23 11:48 PM, Bartosz Golaszewski wrote:
>> On Thu, Oct 5, 2023 at 9:43 PM Dipen Patel <dipenp@nvidia.com> wrote:
>>>
>>> On 10/5/23 12:05 PM, Bartosz Golaszewski wrote:
>>>> On Thu, Oct 5, 2023 at 8:12 PM Dipen Patel <dipenp@nvidia.com> wrote:
>>>>>
>>>>> On 10/5/23 6:48 AM, Bartosz Golaszewski wrote:
>>>>>> On Thu, Oct 5, 2023 at 1:52 AM Dipen Patel <dipenp@nvidia.com> wrote:
>>>>>>>
>>>>>>> On 10/4/23 3:54 PM, Dipen Patel wrote:
>>>>>>>> On 10/4/23 1:33 PM, Dipen Patel wrote:
>>>>>>>>> On 10/4/23 1:30 PM, Dipen Patel wrote:
>>>>>>>>>> On 10/4/23 5:00 AM, Bartosz Golaszewski wrote:
>>>>>>>>>>> On Thu, Sep 7, 2023 at 9:28 AM Linus Walleij <linus.walleij@linaro.org> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> On Tue, Sep 5, 2023 at 8:53 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>>>>>>>>>>>>>
>>>>>>>>>>>>> Using struct gpio_chip is not safe as it will disappear if the
>>>>>>>>>>>>> underlying driver is unbound for any reason. Switch to using reference
>>>>>>>>>>>>> counted struct gpio_device and its dedicated accessors.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>>>>>>>>>>>>
>>>>>>>>>>>> As Andy points out add <linux/cleanup.h>, with that fixed:
>>>>>>>>>>>> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
>>>>>>>>>>>>
>>>>>>>>>>>> I think this can be merged into the gpio tree after leaving some
>>>>>>>>>>>> slack for the HTE maintainer to look at it, things look so much
>>>>>>>>>>>> better after this.
>>>>>>>>>>>>
>>>>>>>>>>>> Yours,
>>>>>>>>>>>> Linus Walleij
>>>>>>>>>>>
>>>>>>>>>>> Dipen,
>>>>>>>>>>>
>>>>>>>>>>> if you could give this patch a test and possibly ack it for me to take
>>>>>>>>>>> it through the GPIO tree (or go the immutable tag from HTE route) then
>>>>>>>>>>> it would be great. This is the last user of gpiochip_find() treewide,
>>>>>>>>>>> so with it we could remove it entirely for v6.7.
>>>>>>>>>>
>>>>>>>>>> Progress so far for the RFT...
>>>>>>>>>>
>>>>>>>>>> I tried applying the patch series on 6.6-rc1 and it did not apply cleanly,
>>>>>>>>>> some patches I needed to manually apply and correct. With all this, it failed
>>>>>>>>>> compilation at some spi/spi-bcm2835 driver. I disabled that and was able to
>>>>>>>>>> compile. I thought I should let you know this part.
>>>>>>>>>>
>>>>>>>>>> Now, I tried to test the hte and it seems to fail finding the gpio device,
>>>>>>>>>> roughly around this place [1]. I thought it would be your patch series so
>>>>>>>>>> tried to just use 6.6rc1 without your patches and it still failed at the
>>>>>>>>>> same place. I have to trace back now from which kernel version it broke.
>>>>>>>>>
>>>>>>>>> [1].
>>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/pateldipen1984/linux.git/tree/drivers/hte/hte-tegra194.c?h=for-next#n781
>>>>>>>>>
>>>>>>>>> of course with your patches it would fail for the gdev instead of the chip.
>>>>>>>>
>>>>>>>> Small update:
>>>>>>>>
>>>>>>>> I put some debugging prints in the gpio match function in the hte-tegra194.c as
>>>>>>>> below:
>>>>>>>>
>>>>>>>> static int tegra_gpiochip_match(struct gpio_chip *chip, void *data)
>>>>>>>>  {
>>>>>>>> +       struct device_node *node = data;
>>>>>>>> +       struct fwnode_handle *fw = of_node_to_fwnode(data);
>>>>>>>> +       if (!fw || !chip->fwnode)
>>>>>>>> +               pr_err("dipen patel: fw is null\n");
>>>>>>>>
>>>>>>>> -       pr_err("%s:%d\n", __func__, __LINE__);
>>>>>>>> +       pr_err("dipen patel, %s:%d: %s, %s, %s, match?:%d, fwnode name:%s\n",
>>>>>>>> __func__, __LINE__, chip->label, node->name, node->full_name, (chip->fwnode ==
>>>>>>>> fw), fw->dev->init_name);
>>>>>>>>         return chip->fwnode == of_node_to_fwnode(data);
>>>>>>>>  }
>>>>>>>>
>>>>>>>> The output of the printfs looks like below:
>>>>>>>> [    3.955194] dipen patel: fw is null -----> this message started appearing
>>>>>>>> when I added !chip->fwnode test in the if condition line.
>>>>>>>>
>>>>>>>> [    3.958864] dipen patel, tegra_gpiochip_match:689: tegra234-gpio, gpio,
>>>>>>>> gpio@c2f0000, match?:0, fwnode name:(null)
>>>>>>>>
>>>>>>>> I conclude that chip->fwnode is empty. Any idea in which conditions that node
>>>>>>>> would be empty?
>>>>>>>
>>>>>>> sorry for spamming, one last message before I sign off for the day....
>>>>>>>
>>>>>>> Seems, adding below in the tegra gpio driver resolved the issue I am facing, I
>>>>>>> was able to verify your patch series.
>>>>>>>
>>>>>>> diff --git a/drivers/gpio/gpio-tegra186.c b/drivers/gpio/gpio-tegra186.c
>>>>>>> index d87dd06db40d..a56c159d7136 100644
>>>>>>> --- a/drivers/gpio/gpio-tegra186.c
>>>>>>> +++ b/drivers/gpio/gpio-tegra186.c
>>>>>>> @@ -989,6 +989,8 @@ static int tegra186_gpio_probe(struct platform_device *pdev)
>>>>>>>                 offset += port->pins;
>>>>>>>         }
>>>>>>>
>>>>>>> +       gpio->gpio.fwnode = of_node_to_fwnode(pdev->dev.of_node);
>>>>>>> +
>>>>>>>         return devm_gpiochip_add_data(&pdev->dev, &gpio->gpio, gpio);
>>>>>>>  }
>>>>>>>
>>>>>>> Now, few follow up questions:
>>>>>>> 1) is this the correct way of setting the chip fwnode in the gpio driver?
>>>>>>
>>>>>> You shouldn't need this. This driver already does:
>>>>>>
>>>>>>     gpio->gpio.parent = &pdev->dev;
>>>>>>
>>>>>> so fwnode should be assigned in gpiochip_add_data_with_key(). Can you
>>>>>> check why this doesn't happen?
>>>>>
>>>>> I do not see anywhere chip->fwnode being set in the gpiochip_add_* function.
>>>>> The only reference I see is here [1]. Does it mean I need to change my match
>>>>> function from:
>>>>>
>>>>> chip->fwnode == of_node_to_fwnode(data)
>>>>>
>>>>> to:
>>>>> dev_fwnode(chip->parent) == of_node_to_fwnode(data)?
>>>>
>>>> No! chip->fwnode is only used to let GPIOLIB know which fwnode to
>>>> assign to the GPIO device (struct gpio_device).
>>> What do you suggest I should use for the match as I do not see chip->fwnode
>>> being set?
>>>
>>
>> This is most likely going to be a longer discussion. I suggest that in
>> the meantime you just assign the gc->fwnode pointer explicitly from
>> the platform device in the tegra GPIO driver and use it in the lookup
>> function. Note that this is NOT wrong or a hack. It's just that most
>> devices don't need to be looked up using gpio_device_find().
> 
> Sure, at the same time, I am also find to use any other method/s.

(Correction) I am also fine*

With patch
https://patchwork.ozlabs.org/project/linux-gpio/patch/20231009173858.723686-1-dipenp@nvidia.com/

Tested-by: Dipen Patel <dipenp@nvidia.com>

>>
>> Bart
>>
>>>>
>>>> Bart
>>>>
>>>>>
>>>>> [1]:
>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib.c?h=v6.6-rc1#n767
>>>>>
>>>>>>
>>>>>> Bart
>>>>>>
>>>>>>> 2) Or should I use something else in hte matching function instead of fwnode so
>>>>>>> to avoid adding above line in the gpio driver?
>>>>>>>
>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Bart
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>
>>>
>