linux-kernel - Re: [PATCH] pinctrl: aspeed: Allow changing hardware strap defaults

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Date:   Wed, 4 Oct 2023 19:27:38 -0700
From:   Zev Weiss <zev@...ilderbeest.net>
To:     Andrew Jeffery <andrew@...econstruct.com.au>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Joel Stanley <joel@....id.au>, linux-aspeed@...ts.ozlabs.org,
        openbmc@...ts.ozlabs.org, linux-gpio@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: aspeed: Allow changing hardware strap defaults

On Wed, Oct 04, 2023 at 06:17:50PM PDT, Andrew Jeffery wrote:
>On Wed, 2023-10-04 at 00:16 -0700, Zev Weiss wrote:
>> Previously we've generally assumed that the defaults in the hardware
>> strapping register are in fact appropriate for the system and thus
>> have avoided making any changes to its contents (with the exception of
>> the bits controlling the GPIO passthrough feature).
>>
>> Unfortunately, on some platforms corrections from software are
>> required as the hardware strapping is simply incorrect for the system
>> (such as the SPI1 interface being configured for passthrough mode when
>> master mode is in fact the only useful configuration for it).  We thus
>> remove the checks preventing changes to the strap register so that the
>> pinctrl subsystem can be used for such corrections.
>
>So the strapping for the SPI1 configuration seems to be prone to
>(copy/paste?) mistakes. Is there evidence that motivates dropping all
>the protection instead of poking a hole for SPI1 like we did for the
>passthrough GPIOs?
>
>I'm still a little attached to the policy that software should be
>beholden to the strapping, and to try to mitigate software mistakes
>given the smattering of bits required to drive the Aspeed pinmux.
>

I have no idea what else might be lurking out there so I took a broader 
(perhaps overly heavy-handed) approach, but the SPI1 mode bits are the 
only ones I've personally encountered being strapped wrong, so sure, I'd 
be fine with just extending the "hole-punch" a bit to add those bits.  
I'll send a v2 doing that shortly.


Thanks,
Zev