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

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Message-ID: <CAHp75Vd5LdP7+ndresVv5STN2zrC3S5puDhcACyEk7MbLA0hgA@mail.gmail.com>
Date: Sun, 12 Jan 2025 18:11:54 +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 6:07 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.
> >
> > ...
> >
> > >  static const struct regmap_config veml3235_regmap_config = {
> > >     .name = "veml3235_regmap",
> > >     .reg_bits = 8,
> > >     .val_bits = 16,
> > >     .max_register = VEML3235_REG_ID,
> > >     .val_format_endian = REGMAP_ENDIAN_LITTLE,
> > > +   .rd_table = &veml3235_readable_table,
> > > +   .wr_table = &veml3235_writable_table,
> > > +   .volatile_table = &veml3235_volatile_table,
> > > +   .cache_type = REGCACHE_RBTREE,
> >
> > Any specific reason why this is NOT a maple tree?
>
> Hello Andy,
>
> 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?

-- 
With Best Regards,
Andy Shevchenko