linux-kernel - Re: Page select register restrictions in regmap core

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Date: Tue, 18 Jun 2024 18:45:09 +0100
From: Mark Brown <broonie@...nel.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Armin Wolf <W_Armin@....de>
Subject: Re: Page select register restrictions in regmap core

On Tue, Jun 18, 2024 at 09:14:56AM -0700, Guenter Roeck wrote:

> Anyway, this may be all irrelevant in respect to regmap support.
> It turns out that at least some i801 controllers don't work with the
> access mechanism used by regmap, or maybe the spd5118 chips don't support
> I2C_FUNC_SMBUS_I2C_BLOCK. I already found that those chips don't support
> auto-incrementing the register address and actually reset the address on byte
> reads (i.e., subsequent calls to i2c_smbus_read_byte() always return the data
> from the first register). Since regmap doesn't have a means for me to say
> "don't use I2C_FUNC_SMBUS_I2C_BLOCK even if the controller supports it",
> I may have to drop regmap support entirely anyway. That would be annoying,
> but right now I have no idea how to work around that problem.

You can set the use_single_read and use_single_write flags in the config
to ensure registers are accessed one at a time, that restriction is
moderately common.

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