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

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Message-ID: <Z4pktkZ1ihfkZjHm@smile.fi.intel.com>
Date: Fri, 17 Jan 2025 16:09:58 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Marek Szyprowski <m.szyprowski@...sung.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 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?

-- 
With Best Regards,
Andy Shevchenko