linux-kernel - Re: [PATCH 1/4] hwmon: (asus-ec-sensors) introduce ec_board

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Message-ID: <CAB95QAQGWRT=UsXPn65oiiwBRa1RKj61sg7wq9d7VntnFWzaOg@mail.gmail.com>
Date:   Wed, 30 Mar 2022 09:51:24 +0200
From:   Eugene Shalygin <eugene.shalygin@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     darcagn@...tonmail.com, Jean Delvare <jdelvare@...e.com>,
        linux-hwmon@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] hwmon: (asus-ec-sensors) introduce ec_board_info
 struct for board data

On Tue, 29 Mar 2022 at 22:28, Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 3/29/22 12:22, Eugene Shalygin wrote:
> > On Tue, 29 Mar 2022 at 15:44, Guenter Roeck <linux@...ck-us.net> wrote:
> >>>
> >>>    struct ec_sensors_data {
> >>> -     unsigned long board_sensors;
> >>> +     struct ec_board_info board_info;
> >>
> >> Please explain why this needs to be the entire structure and not
> >> just a pointer to it.
> >
> > I marked the board_info array as __initconst assuming that this large
> > array will be unloaded from memory after the init phase, while we keep
> > only a single element. Is that assumption incorrect?
> >
>
> What happens if you build the driver into the kernel and then instantiate
> and de-instantiate it multiple times ?

Sorry, I have no idea because I don't know how to load a built-in
driver multiple times. But since this driver is attached to a
motherboard device, which is persistent and always single, do I need
to consider such a scenario?

>
> >>> +static int sensor_count(const struct ec_board_info *board)
> >>> +{
> >>> +     return hweight_long(board->sensors);
> >>> +}
> >>
> >> This function is called several times. Does it really make sense, or is it
> >> necessary, to re-calculate the number of sensors over and over again
> >> instead of keeping it in ec->nr_sensors as before ? What are the benefits ?
> >> Unless there is a good explanation I see that as unrelated and unnecessary
> >> change.
> >
> > This had something to do with data deduplication. However, I need the
> > count value only for looping over the sensor array, thus I can as well
> > add an invalid element to the end of the array. I rushed to submit
> > this driver to replace the wmi one, and it still has an artifact for
> > the WMI code I'd like to get rid of eventually, which is the read
> > buffer and the registers array. This will remove all the nr_ variables
> > and two dynamically allocated arrays. I will understand, of course, if
> > you ask to submit that refactoring separately.
> >
>
> The rule of "one logical change per patch" still applies. If you start
> intermixing parts of future clean-up efforts into current patches, you'll
> see a very unhappy maintainer - especially since this change makes up
> a significant part of this patch, complicates review significantly,
> and makes me wonder if other unrelated changes are included that I don't
> see right now due to all the noise.
>
> Besides, at least in this patch, I don't buy the "deduplication" argument.
> Keeping a single additional variable in a data structure is much simpler
> and straightforward than calling hweight_long() several times. I'd call
> that "complification".

OK, I'll roll it back until I remove the other size variables and arrays.

Best regards,
Eugene