Re: [PATCH 28/57] media: Add ovxxxx_16bit_addr_reg_helpers.h

Hans de Goede
2023-02-10T11:20:26Z

Hi,

On 2/10/23 11:53, Andy Shevchenko wrote:
> On Fri, Feb 10, 2023 at 12:47:55PM +0200, Sakari Ailus wrote:
>> On Fri, Feb 10, 2023 at 12:29:19PM +0200, Laurent Pinchart wrote:
>>> On Fri, Feb 10, 2023 at 12:21:15PM +0200, Sakari Ailus wrote:
>>>> On Thu, Feb 09, 2023 at 06:11:12PM +0200, Laurent Pinchart wrote:
>
> ...
>
>>>> I took a look at this some time ago, too, and current regmap API is a poor
>>>> fit for CCI devices. CCI works on top of e.g. both I²C and I3C so something
>>>> on top of regmap is a better approach indeed.
>>>
>>> I'm confused, is regmap a poor fit, or a better approach ?
>>
>> I'm proposing having something on top of regmap, but not changing regmap
>> itself.
>
> I don't understand why we can't change regmap? regmap has a facility called
> regmap bus which we can provide specifically for these types of devices. What's
> wrong to see it done?

It is fairly easy to layer the few 16 and 24 bit register accesses over
a standard regmap with 16 bit reg-address and 8 bit reg-data width using
regmap_bulk_write() to still do the write in e.g. a single i2c-transfer.

So if we want regmap for underlying physical layer independence, e.g.
spi / i2c / i3c. we can just use standard regmap with a
cci_write_reg helper on top.

I think that would be the most KISS solution here. One thing to also keep
in mind is the amount of work necessary to convert existing sensor drivers.
Also keeping in mind that it is not just the in tree sensor drivers, but
also all out of tree sensor drivers which I have seen use similar constructs.

Requiring drivers to have a list / array of structs of all used register
addresses + specifying the width per register address is not going to scale
very poorly wrt converting all the code out there and I'm afraid that
letting regmap somehow deal with the register-width issue is going to
require something like this.

Regards,

Hans