Hi Andy,

On Tue, 2021-06-01 at 18:24 +0300, Andy Shevchenko wrote:

On Tue, Jun 1, 2021 at 2:49 PM Michael Walle [off-list ref] wrote:

quoted

Am 2021-05-31 17:48, schrieb Andy Shevchenko:

quoted

On Mon, May 31, 2021 at 6:33 PM Sander Vanheule [off-list ref]
wrote:

quoted

On Mon, 2021-05-31 at 14:16 +0300, Andy Shevchenko wrote:

quoted

On Monday, May 31, 2021, Michael Walle [off-list ref] wrote:

quoted

Am 2021-05-31 10:36, schrieb Sander Vanheule:

quoted

Am I missing something here? It seems to me like the regmap interface
can't
really accommodate what's required, unless maybe the rtl8231 regmap
users
perform some manual locking. This all seems terribly complicated
compared to
using an internal output-value cache inside regmap-gpio.

Have you had a chance to look into the PCA953x driver?
Sounds to me that you are missing the APIs that regmap provides.

What would that be? The register cache? We need to cache the
value somehow, because (still assuming it is write only) we cannot
read it back. Thus the read of the RMW, would need get the
value from the cache. Thus the user of gpio-regmap would need
to make sure, to (a) use a cache for the regmap supplied to
gpio-regmap and (b) populate its initial values correctly. Is
that what you are suggesting? And hopefully, no other user
of the regmap will call regcache_mark_dirty() or something
like that.

I had a quick look at the PCA953x driver but it all its
registers are readable according to the comment on the top
of the file.

Since regmap doesn't have a facility to support the registers _at the
same offset_ with different meaning (depending on data direction), the
only way to handle this (without redesign regmap internals) is to add
specific "pages" via additional bits in the address space. So, let's
say 0 = RW, 1 = RO, 2 = WO. In this case see the following offset
mapping of the hypothetical hardware registers:

REG1 (RW)   0x00 -> 0x000
REG2 (RW)   0x04 -> 0x004
REG3 (RO)   0x08 -> 0x108
REG3 (RW)   0x08 -> 0x208

Then these bits should be masked out. Something similar is done in the
PCA953x driver for extended addresses and autoincrement.

This is what I propose to look at as the starter.

Thank you for clarifying. Essentialy this is then the same solution as an extra
cache in gpio-regmap for the output values, except the cacheing is handled by
the regmap layer.

I think this was the last issue standing, so after I implement this, I'll spin a
v4.

Best,
Sander