linux-kernel - Re: [PATCH 0/2] i2c: tegra: allow compiling out support for Tegra's special constrollers

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Date:   Sun, 16 Jan 2022 22:39:27 +0100
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH 0/2] i2c: tegra: allow compiling out support for Tegra's
 special constrollers

On Sun, Jan 16, 2022 at 09:34:42PM +0300, Dmitry Osipenko wrote:
> 16.01.2022 21:03, Michał Mirosław пишет:
> > On Sun, Jan 16, 2022 at 08:54:08PM +0300, Dmitry Osipenko wrote:
> >> 16.01.2022 19:02, Michał Mirosław пишет:
> >>> To patches that, combined, reduce I2C driver's code by ~2kB and a bit
> >>> from runtime overhead for non-Tegra20 or non-Tegra210 builds.
> >>>
> >>> Michał Mirosław (2):
> >>>   i2c: tegra: allow DVC support to be compiled out
> >>>   i2c: tegra: allow VI support to be compiled out
> >>>
> >>>  drivers/i2c/busses/Kconfig     | 16 ++++++++++++++++
> >>>  drivers/i2c/busses/i2c-tegra.c | 35 +++++++++++++++++++++-------------
> >>>  2 files changed, 38 insertions(+), 13 deletions(-)
> >>>
> >>
> >> 2KB is a too small difference to justify the ifdefs and Kconfig entries,
> >> IMO.
> > 
> > Maybe I should have mentioned that it's ~20%? With my "embedded" hat on:
> > I think it might be small, but sometimes it is the difference between
> > bootable kernel or one too big.
> 
> 10KB is a small size too. I'm very doubtful that such changes make any
> real difference in practice.
> 
> Much more practical should be to modularize more kernel code. You should
> be able to squeeze zImage down to 3MB without any code changes by
> toggling more kernel config options to =m. Try to use grate_defconfig
> [1] for the base, that is what postmarketOS kernel build uses.

For normal system this solution is workable. But for recovery, where you
have to fit kernel+initrd in whatever small partition is provided (like
eg. in Transformers 8MiB), it becomes a problem from time to time.
(In this case, modules make it worse due to additional overhead in
kernel and userspace).

Best Regards
Michał Mirosław