linux-kernel - Re: [PATCH 2/2] regmap: sdw: Remove 8-bit value size restriction

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Message-ID: <4a6ae9b4-2748-c751-aec6-05979de95cfe@linux.intel.com>
Date:   Thu, 12 Jan 2023 14:19:29 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Charles Keepax <ckeepax@...nsource.cirrus.com>, vkoul@...nel.org,
        yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        linux-kernel@...r.kernel.org, patches@...nsource.cirrus.com
Subject: Re: [PATCH 2/2] regmap: sdw: Remove 8-bit value size restriction



On 1/12/23 13:50, Mark Brown wrote:
> On Thu, Jan 12, 2023 at 12:43:46PM -0600, Pierre-Louis Bossart wrote:
>> On 1/12/23 12:14, Mark Brown wrote:
> 
>>> The regmap gather_write() operation allows the bus to take two buffers,
>>> one for the register and one for the value, rather than requiring the
>>> core combine everything into a single buffer (mainly useful for large
>>> transfers like firmware downloads).
> 
>> Right, but that's not supported in SoundWire. sdw_nwrite() will only
>> work with consecutive addresses - and the auto-increment is handled in
>> software, not hardware.
> 
> No, that's exactly what this is for.  It's for the *register address*
> being in a separate buffer, the data is then a sequence of consecutive
> register values.>
>> What's suggested here is to use the first element of reg_buf, which begs
>> the question how different this is from a regular write. If there was a
>> discontinuity in reg_buf then this wouldn't work at all.
> 
> reg_buf contains the address of exactly one register.

So what's the difference with a plain write() of N data?