Re: [PATCH v4 1/1] regmap: Synchronize cache for the page selector

[Marek Szyprowski]

On 18.02.2026 10:57, Andy Shevchenko wrote:
> On Wed, Feb 18, 2026 at 09:30:41AM +0100, Marek Szyprowski wrote:
>> On 18.02.2026 08:46, Andy Shevchenko wrote:
>>> If the selector register is represented in each page, its value
>>> according to the debugfs is stale because it gets synchronized
>>> only after the real page switch happens. Hence the regmap cache
>>> initialisation from the HW inherits outdated data in the selector
>>> register.
>>>
>>> Synchronize cache for the page selector just in time.
>>>
>>> Before (offset followed by hexdump, the first byte is selector):
>>>
>>>       // Real registers
>>>       18: 05 ff 00 00 ff 0f 00 00 f0 00 00 00
>>>       ...
>>>       // Virtual (per port)
>>>       40: 05 ff 00 00 e0 e0 00 00 00 00 00 1f
>>>       50: 00 ff 00 00 e0 e0 00 00 00 00 00 1f
>>>       60: 01 ff 00 00 ff ff 00 00 00 00 00 00
>>>       70: 02 ff 00 00 cf f3 00 00 00 00 00 0c
>>>       80: 03 ff 00 00 00 00 00 00 00 00 00 ff
>>>       90: 04 ff 00 00 ff 0f 00 00 f0 00 00 00
>>>
>>> After:
>>>
>>>       // Real registers
>>>       18: 05 ff 00 00 ff 0f 00 00 f0 00 00 00
>>>       ...
>>>       // Virtual (per port)
>>>       40: 00 ff 00 00 e0 e0 00 00 00 00 00 1f
>>>       50: 01 ff 00 00 e0 e0 00 00 00 00 00 1f
>>>       60: 02 ff 00 00 ff ff 00 00 00 00 00 00
>>>       70: 03 ff 00 00 cf f3 00 00 00 00 00 0c
>>>       80: 04 ff 00 00 00 00 00 00 00 00 00 ff
>>>       90: 05 ff 00 00 ff 0f 00 00 f0 00 00 00
>>>
>>> Fixes: 6863ca622759 ("regmap: Add support for register indirect addressing.")
>>> Signed-off-by: Andy Shevchenko<andriy.shevchenko@xxxxxxxxxxxxxxx>
>>> ---
>>> v4: reworked the approach completely
>>>
>>> Marek, Dmitry,
>>> Please, test on your HW to be sure this will have no side effects
>>> in your case with LT9611.
>> It looks that it ends in infinite recurrent calls after this patch:
> Thank you for the prompt testing! Can you also _add_ the patch on top from
> https://lore.kernel.org/all/Z4ppo8wV3nicOfAQ@xxxxxxxxxxxxxxxxxx/ ?

I've applied that change and the driver fails with the following messages:

# dmesg | grep lt96
lt9611uxc 5-002b: LT9611 revision: 0x00.00.00
lt9611uxc 5-002b: LT9611 version: 0x00
lt9611uxc 5-002b: FW version 0, enforcing firmware update
lt9611uxc 5-002b: Direct firmware load for lt9611uxc_fw.bin failed with 
error -2
lt9611uxc 5-002b: probe with driver lt9611uxc failed with error -2

Maybe this driver simply doesn't use this regmap feature properly and 
there is no point trying to fix regmap?

>> Insufficient stack space to handle exception!
>> ESR: 0x0000000096000047 -- DABT (current EL)
>> FAR: 0xffff8000859bffe0
>> Task stack:     [0xffff8000859c0000..0xffff8000859c4000]
>> IRQ stack:      [0xffff800080030000..0xffff800080034000]
>> Overflow stack: [0xffff0001fef36140..0xffff0001fef37140]
>> CPU: 6 UID: 0 PID: 341 Comm: (udev-worker) Not tainted
>> 6.19.0-next-20260217+ #12215 PREEMPT
>> Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
>> pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>> pc : _regmap_select_page+0x4/0x120
>> lr : _regmap_raw_read+0x240/0x340

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland