linux-kernel - Re: [PATCH] gpiolib: Show correct direction from the beginning

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Message-ID: <27c8e13a-44bf-18b5-083b-25b87d7b8605@kernel.org>
Date:   Thu, 20 Sep 2018 21:05:21 -0500
From:   Timur Tabi <timur@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Show correct direction from the beginning

On 9/20/18 5:36 PM, Linus Walleij wrote:
> What I mean is that $SUBJECT patch might not hurt Qualcomms
> GPIOs (not crash the platform) if and only if it is augmented to not
> try to get the initial direction from lines masked off in .valid_mask
> if .need_valid_mask is true.
> 
> Whether it makes sense semantically is a different debate, but it
> seems possible to reintroduce calling .get_direction() without
> hurting anyone.

That means that all the logic for checking valid_mask needs to be added 
to the chip driver's .get_direction() function.  We can add that logic 
to msm_gpio_get_direction (at one point, I had a patch that did that, 
but it was rejected).

My concern is: what if a driver depends on a .request call being made 
(in order to configure muxes, for example) before touching the hardware?

I wonder if this is something that really should be handled in the 
driver's .probe function.  The driver should collect that information 
and pass it to add_data.