linux-kernel - Re: [PATCH v2 6/7] platform: x86: Add intel_skl

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Date:   Tue, 19 Jan 2021 18:36:31 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Daniel Scally <djrscally@...il.com>, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-i2c@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        devel@...ica.org, rjw@...ysocki.net, lenb@...nel.org,
        andy@...nel.org, mika.westerberg@...ux.intel.com,
        linus.walleij@...aro.org, bgolaszewski@...libre.com,
        wsa@...nel.org, lee.jones@...aro.org, hdegoede@...hat.com,
        mgross@...ux.intel.com, robert.moore@...el.com,
        erik.kaneda@...el.com, sakari.ailus@...ux.intel.com,
        kieran.bingham@...asonboard.com
Subject: Re: [PATCH v2 6/7] platform: x86: Add intel_skl_int3472 driver

Hi Andy,

On Tue, Jan 19, 2021 at 11:33:58AM +0200, Andy Shevchenko wrote:
> On Tue, Jan 19, 2021 at 12:11:40AM +0000, Daniel Scally wrote:
> > On 18/01/2021 21:19, Daniel Scally wrote:
> >
> > I'm more and more confident that this will work, but it has some
> > knock-on effects:
> > 
> > The both clk and regulator gpio driver expects to be able to fetch the
> > GPIO using devm_gpiod_get(&pdev->dev, "enable", ...). That won't work of
> > course, so we need to add another GPIO lookup table so those drivers can
> > see the GPIOs. For that, we need to know what dev_name(&pdev->dev) will
> > be so we can set the .dev_id member of a gpiod_lookup_table to that
> > value, but that isn't set until _after_ the pdev is registered (because
> > it has to figure out the id, we can't manually set the IDs because there
> > could be more than one instance of int3472-discrete bound to multiple
> > PMIC devices, and we don't know which id the current one should have).
> > Finally, we can't wait until the device is registered because it
> > immediately probes, can't find the GPIO and then fails probe.
> > 
> > It's similar problem that causes us to need the i2c-acpi name format
> > macros, but complicated by the dynamic ID part of dev_name(&pdev->dev)
> > 
> > Solving it is a bit of a sticky one; perhaps something like moving the
> > dev_set_name() part of platform_device_add() [1] to its own function,
> > that's called in both platform_device_alloc() and
> > platform_device_register(). That way it would be available before the
> > device itself was registered, meaning we could create the lookup table
> > before it probes the driver.
> 
> See my previous reply. TL;DR: you have to modify clk-gpio.c to export couple of
> methods to be able to use it as a library.

That seems really overkill given the very simple implementation of the
clock provided here.

> > (also, Laurent, if we did it this way we wouldn't be able to also handle
> > the led-indicator GPIO here without some fairly major rework)
> 
> LED indicators are done as LED class devices (see plenty of examples in PDx86
> drivers: drivers/platform/x86/)

How do you expose the link between the sensor and its indicator LED to
userspace ? Isn't it better to handle it in the kernel to avoid rogue
userspace turning the camera on without notifying the user ?

-- 
Regards,

Laurent Pinchart