linux-kernel - Re: [PATCH v2 3/4] iio: light: veml3235: extend regmap to add cache

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Message-ID: <CAHp75Ven01nuqM=PXpPN+XHi1r8AS=j7kRM16KtvAr1kZbjvfQ@mail.gmail.com>
Date: Sun, 12 Jan 2025 20:50:41 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>
Cc: Matti Vaittinen <mazziesaccount@...il.com>, Jonathan Cameron <jic23@...nel.org>, 
	Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v2 3/4] iio: light: veml3235: extend regmap to add cache

On Sun, Jan 12, 2025 at 6:21 PM Javier Carrasco
<javier.carrasco.cruz@...il.com> wrote:
> On Sun Jan 12, 2025 at 5:11 PM CET, Andy Shevchenko wrote:
> > On Sun, Jan 12, 2025 at 6:07 PM Javier Carrasco
> > <javier.carrasco.cruz@...il.com> wrote:
> > > On Sun Jan 12, 2025 at 4:18 PM CET, Andy Shevchenko wrote:
> > > > Tue, Dec 24, 2024 at 11:59:02AM +0100, Javier Carrasco kirjoitti:
> > > > > The configuration and ID registers are not volatile and are not affected
> > > > > by read operations (i.e. not precious), making them suitable to be
> > > > > cached in order to reduce the number of accesses to the device.

...

> > > > > +   .cache_type = REGCACHE_RBTREE,
> > > >
> > > > Any specific reason why this is NOT a maple tree?
> > >
> > > I followed the most common approach in IIO (52 RBTREE vs 2 MAPLE),
> >
> > But it's historical and can't be taken as an argument.
> >
> > > assuming that the "low-end systems" comment for the different REGCACHE_*
> > > applies well to the typical systems that will make use of this driver,
> > > and many others under IIO. I considered that *possible* performance
> > > advantage for low-end systems above other considerations, like the
> > > general rule about using maple tree.
> >
> > https://elixir.bootlin.com/linux/v6.13-rc3/source/include/linux/regmap.h#L58
> >
> > "Any new caches
> >  * should usually use the maple tree cache unless they specifically
> >  * require that there are never any allocations at runtime and can't
> >  * provide defaults in which case they should use the flat cache."
> >
> > Can you reconsider?
>
> That was exactly the comment I referenced, actually the part about
> low-end systems that appears right after what you highlighted.
>
> I have nothing against switching to MAPLE, if that is preferred even if
> the main user of this driver will be a low-end system. I think that IIO
> is a typical subsystem that addresses needs for very low-end systems
> that are sometimes slightly more powerful than a microcontroller, but on
> the other hand I am by no means an expert, and if MAPLE is the way to go
> here as well, I will send a follow-up patch for it.

Ah, I see now. Okay, I leave it then to Jonathan as I am okay with any
choice as long as it's understood and justified.


-- 
With Best Regards,
Andy Shevchenko