linux-kernel - Re: [PATCH 01/16] gpio: dwapb: Use modern PM macros

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Message-ID: <aKdNBhpNofchexgb@xhacker>
Date: Fri, 22 Aug 2025 00:44:54 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Michael Büsch <mb@...s.ch>,
	Doug Berger <opendmb@...il.com>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>, Michael Buesch <m@...s.ch>,
	Hoan Tran <hoan@...amperecomputing.com>,
	Andy Shevchenko <andy@...nel.org>, Daniel Palmer <daniel@...ngy.jp>,
	Romain Perier <romain.perier@...il.com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Kevin Hilman <khilman@...nel.org>,
	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Shubhrajyoti Datta <shubhrajyoti.datta@....com>,
	Srinivas Neeli <srinivas.neeli@....com>,
	Michal Simek <michal.simek@....com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	linux@...tq-group.com
Subject: Re: [PATCH 01/16] gpio: dwapb: Use modern PM macros

On Wed, Aug 20, 2025 at 10:04:39PM +0300, Andy Shevchenko wrote:
> On Wed, Aug 20, 2025 at 8:11 PM Michael Büsch <mb@...s.ch> wrote:
> >
> > On Wed, 20 Aug 2025 19:54:44 +0300
> > Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> >
> > > > The dwapb_context structure is always embedded into struct
> > > > dwapb_gpio_port to simplify code. Sure this brings a tiny 36 bytes
> > > > data overhead for !CONFIG_PM_SLEP.
> > >
> > > I don't think it's a good approach to add a lot of data for peanuts in
> > > case of PM_SLEEP=n.
> >
> > It wastes 36 bytes in case of PM=n.
> 
> ...per port.
> 
> > The driver currently allocates the struct with kzalloc and stores a pointer to it
> > in case of PM=y.
> > So this probably has an overhead in the same order of magnitude (pointer +
> > malloc overhead/alignment/fragmentation) in case of PM=y now.
> 
> ...per driver.

Before the patch, struct dwapb_context *ctx is also per port.

> 
> So, I can't say it's equal, but I leave this to maintainers to decide,

What in my mind now: this is linux rather than RTOS. After greping the
the arm/arm64/riscv dts dir, the max port number is 6, the berlin2q
soc families, so this means current we have wasted 216 bytes memory which
is trivial compared to the system memory.