linux-kernel - Re: [PATCH v2 2/2] gpio: mmio: Use new flag BGPIOF_NO

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Date:   Mon, 13 Mar 2023 13:56:24 +0000
From:   "Leonard, Niall" <Niall.Leonard@....com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] gpio: mmio: Use new flag BGPIOF_NO_INPUT.

On 12/02/2023 12:38, Andy Shevchenko wrote:
> *External Message* - Use caution before opening links or attachments
> 
> On Tue, Jan 31, 2023 at 01:49:38PM +0000, Niall Leonard wrote:
>> Add new flag BGPIOF_NO_INPUT to header file.
>> Use the existing shadow data register 'bgpio_data' to allow
>> the last written value to be returned by the read operation
>> when BGPIOF_NO_INPUT flag is set.
>> Ensure this change only applies to the specific binding "wd,mbl-gpio".
> 
> I'm wondering why do we need that.
> 
> I mean the reading back the (possible cached) output value is the right thing
> to do by default for GPIO (in output mode) or GPO. So, instead you can simply
> check the current direction of the pin and return (cached) value.
> 
> Or did I miss something?
> 
My thinking here was that I don't want to break any existing code which 
relies on the read always reading the physical port.
I'm going to rethink my approach here as I'm starting to think the 
better approach would be to modify the gpio-74xx-mmio.c driver to cater 
for this hardware.

Regards,
Niall.