linux-kernel - Re: [PATCH v3] pinctrl: mcp23s08: init reg_defaults from HW at probe and switch cache type

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Message-ID: <aP9cSArwCdvPZff3@smile.fi.intel.com>
Date: Mon, 27 Oct 2025 13:49:28 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: bigunclemax@...il.com
Cc: linux-gpio@...r.kernel.org, akaessens@...il.com,
	arturas.moskvinas@...il.com, e.shatokhin@...ro.com,
	linus.walleij@...aro.org, linux-kernel@...r.kernel.org,
	mastichi@...il.com, mike.looijmans@...ic.nl,
	radim.pavlik@...-biometrics.com, u.kleine-koenig@...gutronix.de,
	zou_wei@...wei.com, Sander Vanheule <sander@...nheule.net>
Subject: Re: [PATCH v3] pinctrl: mcp23s08: init reg_defaults from HW at probe
 and switch cache type

On Mon, Oct 27, 2025 at 01:46:26PM +0300, bigunclemax@...il.com wrote:
> 
> The probe function does not guarantee that chip registers are in their
> default state. Thus using reg_defaults for regmap is incorrect.
> 
> For example, the chip may have already been configured by the bootloader
> before the Linux driver loads, or the mcp might not have a reset at all
> and not reset a state between reboots.
> 
> In such cases, using reg_defaults leads to the cache values diverging
> from the actual registers values in the chip.
> 
> Previous attempts to fix consequences of this issue were made in
> 'commit 3ede3f8b4b4b ("pinctrl: mcp23s08: Reset all pins to input at
> probe")', but this is insufficient. The OLAT register reset is also
> required. And there's still potential for new issues arising due to cache
> desynchronization of other registers.
> 
> Therefore, remove reg_defaults and provide num_reg_defaults_raw. In that
> case the cache defaults being initialized from hardware.
> 
> Also switch cache type to REGCACHE_MAPLE, which is aware of (in)valid
> cache entries.
> 
> And remove the force reset all pins to input at probe as it is no longer
> required.

> ---

No changelog? No need to resend, just reply with the missing piece.

>  drivers/pinctrl/pinctrl-mcp23s08.c | 40 +++---------------------------
>  1 file changed, 4 insertions(+), 36 deletions(-)

-- 
With Best Regards,
Andy Shevchenko