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

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Date:   Thu, 12 Jan 2023 12:43:46 -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 12:14, Mark Brown wrote:
> On Thu, Jan 12, 2023 at 11:38:38AM -0600, Pierre-Louis Bossart wrote:
> 
>>> +static int regmap_sdw_gather_write(void *context,
>>> +				   const void *reg_buf, size_t reg_size,
>>> +				   const void *val_buf, size_t val_size)
>>>  {
>>>  	struct device *dev = context;
>>>  	struct sdw_slave *slave = dev_to_sdw_dev(dev);
>>> -	int read;
>>> +	u32 addr = le32_to_cpu(*(const __le32 *)reg_buf);
> 
>> what's the difference between regmap_sdw_write() and
>> regmap_sdw_gather_write()? Seems to me that it's the same functionality
>> of writing at consecutive addresses. It's not a true 'gather' in the
>> sense that only the first address is used?
> 
> 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.

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.