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

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Message-ID: <b5f70864-baf9-4590-880d-96727b7b80cb@sirena.org.uk>
Date: Tue, 6 Jan 2026 15:12:23 +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 Tue, Jan 06, 2026 at 07:38:26PM +0530, Sheetal . wrote:

> 2. No functional benefit: Entries like { REG, 0x0 } only set the
>    validity bit; the cache value is already zero.

For sparse caches specifying the register also allocates the cache
entry.

> Add a cache_default_is_zero flag to struct regmap_config. When set,
> the flat cache marks registers as valid on first read instead of
> warning. This ensures only accessed registers are marked valid,

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

> index b0b9be750d93..bf918f88bfd3 100644
> --- a/include/linux/regmap.h
> +++ b/include/linux/regmap.h
> @@ -452,6 +452,7 @@ struct regmap_config {
>  	enum regcache_type cache_type;
>  	const void *reg_defaults_raw;
>  	unsigned int num_reg_defaults_raw;
> +	bool cache_default_is_zero;

It would be better if this were something specific to the flat cache
since otherwise we have to consider what this means for the other cache
types.

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