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

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Date: Tue, 18 Jun 2024 10:01:47 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Mark Brown <broonie@...nel.org>
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

Hi Mark,

On 6/18/24 09:14, Guenter Roeck wrote:
[ ... ]
>> So surely this means that the entire register map is one window and
>> there's no point in defining two ranges?  Those registers are paged with
>> the same selector as the other registers.  At which point you can just
>> sidestep the issue and be like the other current problematic drivers.
>>
> 
> Just define a single range covering the entire window ? That might actually
> work if I manipulate the nvmem addresses such that they always point to the
> upper 64 bytes. I'll give that a try.
> 

Excellent, that worked. Thanks a lot, and sorry for being slow in understanding
what I needed to do.

[ ... ]
> 
> 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.
> 

I think I found a workaround for that problem: All I needed to do
was to define a regmap bus with its own read and write functions.
Please let me know if there is a better way to solve that problem.

Thanks,
Guenter