linux-kernel - Re: [PATCH v2 3/3] platform/chrome: cros_ec

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Date: Thu, 28 Mar 2024 02:32:28 +0000
From: Pavan Holla <pholla@...omium.org>
To: krzk@...nel.org
Cc: abhishekpandit@...omium.org,
	bleung@...omium.org,
	chrome-platform@...ts.linux.dev,
	gregkh@...uxfoundation.org,
	groeck@...omium.org,
	heikki.krogerus@...ux.intel.com,
	linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org,
	pholla@...omium.org,
	tzungbi@...nel.org
Subject: Re: [PATCH v2 3/3] platform/chrome: cros_ec_ucsi: Implement UCSI PDC driver

On Tue, Mar 26, 2024 at 9:59 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> On 27/03/2024 04:39, Pavan Holla wrote:
> > Hi Krzysztof,
> >
> > Thanks for the review.
> >
> > On Tue, Mar 26, 2024 at 1:47 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> >> Nothing improved.
> >
> > Yes. I only added maintainers of drivers/platform/chrome in v2. I am
> > still investigating why MODULE_ALIAS() is required.
>
> Heh, I wrote why. You miss ID table.

This driver is going to be used by the cros_ec_dev.c MFD. The UCSI device doesn’t
have an ACPI or OF entry, so I am not sure how I can use MODULE_DEVICE_TABLE
here. If I don’t use MODULE_ALIAS(“platform:” DRV_NAME),
https://elixir.bootlin.com/linux/latest/source/drivers/mfd/cros_ec_dev.c#L206
isn’t able to automatically associate the driver with the device at boot.
I haven’t upstreamed the change in cros_ec_dev.c yet, but the code is similar to
existing code for drivers/platform/chrome/cros_usbpd_logger.c. There are many
other occurrences of the same MODULE_ALIAS pattern:

~/v6.6$ grep -r 'MODULE_ALIAS("platform:" DRV_NAME)' *  | wc -l
93

I am still trying to figure out why the “platform:” string allows cros_ec_dev.c to
load the driver. I suspect it might be due to
https://elixir.bootlin.com/linux/latest/source/drivers/base/platform.c#L1257.

Thanks,
Pavan