linux-kernel - Re: [PATCH 0/2] Fixes for the mcp2221 gpiochip get

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Date:   Thu, 13 Apr 2023 16:49:13 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Louis Morhet <lmorhet@...rayinc.com>
Cc:     gupt21@...il.com, jikos@...nel.org, linux-i2c@...r.kernel.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Fixes for the mcp2221 gpiochip get_* calls

On Apr 04 2023, Louis Morhet wrote:
> The mcp2221 HID driver exposes a gpiochip device.
> While gpioset seemed to work fine, gpioget always returned 1 on all 4
> GPIOs of the component (0x01 for input in the field "direction",
> according to the documentation).
> 
> This patch series addresses this issue by fixing the order of the fields
> in the driver's representation of the chip answer, and adding
> consistency to the way the callbacks prepare their command and the way
> the hid event handler gets these fields.
> The set callbacks use a similar mechanism, but work for now because
> setting a direction/value only requires gpio-specific positioning in the
> command preparation, and not in the raw_event handler.

As you should have seen in the automatic replied, I took that series in
because it seems to fix a rather worrying bug.


> 
> The core of this issue being a discrepancy in the way the command and
> the answer fetch their fields of interest, I would also like to ask if
> we should uniformize a bit the way this driver handles gpio, and how.
> I thought about several possible implementations for that:
> Use mcp->gp_idx as the base offset of the gpio for set too, and modify
> the raw_event handler to fetch all relevant data based on that; or set
> the buffers in the mcp structure as unions of the various commands
> handled and use gp_idx simply as the gpio index to access relevant data
> directly from the structured representation everywhere; or go back to ye
> old defines to ensure portability...

Honestly, it's hard to make a choice here. You haven't got a replied
from the other mcp2221 folks in almost 10 days so I am not sure you'll
get feedback directly.

May I suggest that you work on any one of these idea, and then submit a
series? Generally, having the code ready makes it way easier to decide
if this is a good solution or not, while having 3 different vague
suggestions makes it hard to see the implications of them.

Also, just a side note, this driver is very limited in term of scope, as
it only touches one dedicated device. Which means that whatever solution
feels the more elegant to you has a good chance of being accepted :)

Cheers,
Benjamin

> 
> Louis Morhet (2):
>   HID: mcp2221: fix report layout for gpio get
>   HID: mcp2221: fix get and get_direction for gpio
> 
>  drivers/hid/hid-mcp2221.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> -- 
> 2.17.1
> 
> 
> 
> 
>