linux-kernel - Re: [PATCH v3 1/1] regmap: Synchronize cache for the page selector

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Message-ID: <8a7581e4-6422-4d77-8027-02df0d7da489@samsung.com>
Date: Fri, 17 Jan 2025 17:05:42 +0100
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org, Greg
	Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
	<rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>, DRI mailing list
	<dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v3 1/1] regmap: Synchronize cache for the page selector

On 17.01.2025 15:30, Andy Shevchenko wrote:
> On Fri, Jan 17, 2025 at 04:09:58PM +0200, Andy Shevchenko wrote:
>> On Fri, Jan 17, 2025 at 02:57:52PM +0100, Marek Szyprowski wrote:
>>> On 16.01.2025 13:42, Andy Shevchenko wrote:
>>>> If the selector register is represented in each page, its value
>>>> in accordance to the debugfs is stale because it gets synchronized
>>>> only after the real page switch happens. Synchronize cache for
>>>> the page selector.
>>>>
>>>> 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@...ux.intel.com>
>>> This patch landed in linux-next some time ago as commit 1fd60ed1700c
>>> ("regmap: Synchronize cache for the page selector"). Today I've noticed
>>> that it causes a regression for Lontium LT9611UXC HDMI bridge driver.
>> Is there any datasheet link to the HW in question?
>>
>> (FWIW, I have tested this with the CY8C9540 GPIO I²C expander on Intel Galileo
>>   Gen 1 board.)
>>
>>> With today's linux-next I got the following messages on QCom RB5 board:
>>>
>>> # dmesg | grep  lt9611uxc
>>> [   13.737346] lt9611uxc 5-002b: LT9611 revision: 0x00.00.00
>>> [   13.804190] lt9611uxc 5-002b: LT9611 version: 0x00
>>> [   13.870564] lt9611uxc 5-002b: FW version 0, enforcing firmware update
>>> [   13.877437] lt9611uxc 5-002b: Direct firmware load for
>>> lt9611uxc_fw.bin failed with error -2
>>> [   13.887517] lt9611uxc 5-002b: probe with driver lt9611uxc failed with
>>> error -2
>>>
>>> after reverting the $subject patch, the driver probes fine on that board.
>>>
>>> I'm not sure if this is really a bug caused by this change or simply the
>>> driver already was aligned to old regmap behavior. Dmitry, could you
>>> check the regamp usage and review the changes introduced by this patch?
>>> Let me know if there is anything to check on the real hardware to help
>>> resolving this issue.
>> Yes, see below. And thank you for your report!
>>
>> ...
>>
>>>> +		/*
>>>> +		 * If selector register has been just updated, update the respective
>>>> +		 * virtual copy as well.
>>>> +		 */
>>>> +		if (page_chg &&
>>>> +		    in_range(range->selector_reg, range->window_start, range->window_len))
>>>> +			_regmap_update_bits(map, sel_register, mask, val, NULL, false);
>> Can you add a test printk() here to show
>>
>> page_chg
>> range->selector_reg, range->window_start, range->window_len
>> sel_register, mask, val
>>
>> ?
>>
>> And would commenting these three lines make it work again?
> Also try to apply this patch (while having the above lines not commented):

This patch applied alone doesn't change anything. Probe still fails.

However, with the mentioned 3 lines in the regmap code commented AND 
this patch applied, lt9611uxc driver probe also fails. Does it mean that 
there is really a bug in the driver?

>  From 0fe5fe51d8b86305a4ca1ae44ede34a24fe2f9d7 Mon Sep 17 00:00:00 2001
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Date: Fri, 17 Jan 2025 16:29:19 +0200
> Subject: [PATCH 1/1] TBD:
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>   drivers/gpu/drm/bridge/lontium-lt9611uxc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/lontium-lt9611uxc.c b/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> index f4c3ff1fdc69..35a1dd568bbb 100644
> --- a/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> +++ b/drivers/gpu/drm/bridge/lontium-lt9611uxc.c
> @@ -69,7 +69,7 @@ struct lt9611uxc {
>   static const struct regmap_range_cfg lt9611uxc_ranges[] = {
>   	{
>   		.name = "register_range",
> -		.range_min =  0,
> +		.range_min = 0x0100,
>   		.range_max = 0xd0ff,
>   		.selector_reg = LT9611_PAGE_CONTROL,
>   		.selector_mask = 0xff,

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