linux-kernel - Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver

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Message-ID: <8f1b0a8a-35b2-1d00-c156-74d9ec3058d6@ideasonboard.com>
Date:   Thu, 14 May 2020 14:50:27 +0100
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jacopo Mondi <jacopo@...ndi.org>,
        Niklas Söderlund <niklas.soderlund@...natech.se>,
        Sakari Ailus <sakari.ailus@....fi>,
        Hans Verkuil <hverkuil@...all.nl>,
        Hyun Kwon <hyunk@...inx.com>, Rob Herring <robh+dt@...nel.org>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>
Subject: Re: [PATCH v9 2/4] media: i2c: Add MAX9286 driver

On 14/05/2020 13:48, Manivannan Sadhasivam wrote:
> On Thu, May 14, 2020 at 01:59:35PM +0200, Geert Uytterhoeven wrote:
>> Hi Kieran,
>>
>> On Thu, May 14, 2020 at 1:47 PM Kieran Bingham
>> <kieran.bingham+renesas@...asonboard.com> wrote:
>>> On 14/05/2020 11:13, Manivannan Sadhasivam wrote:
>>>> On Thu, May 14, 2020 at 11:02:53AM +0100, Kieran Bingham wrote:
>>>>> On 12/05/2020 19:17, Manivannan Sadhasivam wrote:
>>>>>> On Tue, May 12, 2020 at 04:51:03PM +0100, Kieran Bingham wrote:
>>>>>>> The MAX9286 is a 4-channel GMSL deserializer with coax or STP input and
>>>>>>> CSI-2 output. The device supports multicamera streaming applications,
>>>>>>> and features the ability to synchronise the attached cameras.
>>>>>>>
>>>>>>> CSI-2 output can be configured with 1 to 4 lanes, and a control channel
>>>>>>> is supported over I2C, which implements an I2C mux to facilitate
>>>>>>> communications with connected cameras across the reverse control
>>>>>>> channel.
>>>>>>>
>>>>>>> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>>>>>>> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>>>>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
>>>>>>> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
>>
>>>>>>> --- /dev/null
>>>>>>> +++ b/drivers/media/i2c/max9286.c
>>
>>>>>>> +static int max9286_register_gpio(struct max9286_priv *priv)
>>>>>>> +{
>>>>>>> +  struct device *dev = &priv->client->dev;
>>>>>>> +  struct gpio_chip *gpio = &priv->gpio;
>>>>>>> +  int ret;
>>>>>>> +
>>>>>>> +  static const char * const names[] = {
>>>>>>> +          "GPIO0OUT",
>>>>>>> +          "GPIO1OUT",
>>>>>>> +  };
>>>>>>> +
>>>>>>> +  /* Configure the GPIO */
>>>>>>> +  gpio->label = dev_name(dev);
>>>>>>
>>>>>> So if you have more than one MAX9286 in a system, all gpiochips will appear
>>>>>> with the same name. I'd recommend to append the index to distinguish properly.
>>>>>
>>>>> Ah yes, that's a good point, and I think I've even seen that.
>>>>>
>>>>> I'll fix it now.
>>>
>>> Oh, in fact actually this doesn't.
>>>
>>> gpiodetect prints:
>>>
>>> gpiochip10 [4-004c] (2 lines)
>>> gpiochip11 [4-006c] (2 lines)
>>>
>>> and mostly references them as gpiochip10 and gpiochip11.
>>
>> Indeed, dev_name() should be different for each instance.
>>
> 
> Ah, my bad! Somehow I got confused that this delivers static name... Sorry for
> the noise, Kieran.
> 
>>> However,
>>>
>>>> [    2.318533] gpio gpiochip11: Detected name collision for GPIO name 'GPIO0OUT'
>>>> [    2.325739] gpio gpiochip11: Detected name collision for GPIO name 'GPIO1OUT'
>>>
>>> That seems to be more of a problem for the gpio library, so I think I'll
>>> just drop the const names. I don't think they add much value.
>>
> 
> Well, I should've pointed this instead of above...
> 
> (lack of coffee)
> 
>> These are the line names.  If they're not unique, a warning is printed,
>> but they are still registered.
>> So probably you want to use kasprintf("%s.%s", dev_name(dev), names[i]) to
>> generate names.
>>
> 
> Ack.
> 
> I think you should CC Linus W for next iteration to get review for gpiolib
> implementation.

Good idea. I think I'll drop the names though for now.

--
Kieran


> 
> Thanks,
> Mani
> 
>> See "[PATCH] gpiolib: Document that GPIO line names are not globally unique"
>> (https://lore.kernel.org/linux-gpio/20200511101828.30046-1-geert+renesas@glider.be/)
>> to clear up the details.
>>
>> Gr{oetje,eeting}s,
>>
>>                         Geert
>>
>> -- 
>> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
>>
>> In personal conversations with technical people, I call myself a hacker. But
>> when I'm talking to journalists I just say "programmer" or something like that.
>>                                 -- Linus Torvalds