linux-kernel - Re: [RFC PATCH 1/2] regmap: Add cache_default_is

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Message-ID: <0ece3e08-3ffc-418c-9e7b-eaf098fb49bc@sirena.org.uk>
Date: Wed, 7 Jan 2026 11:20:26 +0000
From: Mark Brown <broonie@...nel.org>
To: "Sheetal ." <sheetal@...dia.com>
Cc: Sander Vanheule <sander@...nheule.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org,
	linux-tegra@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] regmap: Add cache_default_is_zero flag for flat
 cache

On Wed, Jan 07, 2026 at 12:25:01PM +0530, Sheetal . wrote:
> On 06-01-2026 20:42, Mark Brown wrote:

> > Why do this on first read rather than than just fill the valid flags
> > during initialisation?

> Setting valid bits on first read rather than bitmap_fill() at init ensures:
> - Only accessed registers are marked valid
> - regcache_sync() only syncs registers that were actually used
> - Avoids writes to holes or unused registers during sync
> - Safer for drivers without writeable_reg callback

Seems reasonable, put that in the changelog please.

BTW I forgot in my initial review but please add KUnit coverage for
this, we've got good coverage of the cache code.

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