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

[Dmitry Baryshkov]

On Wed, Jan 29, 2025 at 05:07:52PM +0200, Andy Shevchenko wrote:
> On Tue, Jan 28, 2025 at 06:43:26PM +0200, Andy Shevchenko wrote:
> > On Tue, Jan 28, 2025 at 05:08:08PM +0100, Marek Szyprowski wrote:
> > > On 21.01.2025 14:29, Andy Shevchenko wrote:
> > > > On Tue, Jan 21, 2025 at 08:33:09AM +0100, Marek Szyprowski wrote:
> > > >> On 17.01.2025 18:28, Andy Shevchenko wrote:
> > > >>> On Fri, Jan 17, 2025 at 05:05:42PM +0100, Marek Szyprowski wrote:
> > > >>>
> > > >>> Does it fail in the same way?
> > > >> Yes, the hw revision is reported as zero in this case: LT9611 revision:
> > > >> 0x00.00.00
> > > > Hmm... This is very interesting! It means that the page selector is a bit
> > > > magical there. Dmitry, can you chime in and perhaps shed some light on this?
> > > >
> > > >>>> Does it mean that there is really a bug in the driver?
> > > >>> Without looking at the datasheet it's hard to say. At least what I found so far
> > > >>> is one page of the I²C traffic dump on Windows as an example how to use their
> > > >>> evaluation board and software, but it doesn't unveil the bigger picture. At
> > > >>> least what I think is going on here is that the programming is not so easy as
> > > >>> just paging. Something is more complicated there.
> > > >>>
> > > >>> But at least (and as Mark said) the most of the regmap based drivers got
> > > >>> the ranges wrong (so, at least there is one bug in the driver).
> > > >> I can do more experiments if this helps. Do you need a dump of all
> > > >> regmap accesses or i2c traffic from this driver?
> > > > It would be helpful! Traces from the failed and non-failed cases
> > > > till the firmware revision and chip ID reading would be enough to
> > > > start with.
> > > 
> > > I'm sorry for the delay, I was a bit busy with other stuff.
> > 
> > No problem and thanks for sharing.
> > 
> > > Here are logs (all values are in hex):
> > > 
> > > next-20250128 (probe broken):
> > > root@target:~# dmesg | grep regmap
> > > [   14.817604] regmap_write reg 80ee <- 1
> > > [   14.823036] regmap_read reg 8100 -> 0
> > > [   14.827631] regmap_read reg 8101 -> 0
> > > [   14.832130] regmap_read reg 8102 -> 0
> > 
> > 
> > 
> > > next-20250128 + 1fd60ed1700c reverted (probe okay):
> > > root@target:~# dmesg | grep regmap
> > > [   13.565920] regmap_write reg 80ee <- 1
> > > [   13.567509] regmap_read reg 8100 -> 17
> > > [   13.568219] regmap_read reg 8101 -> 4
> > > [   13.568909] regmap_read reg 8102 -> 93
> > 
> > Something is missing here. Like we have an identical start and an immediate
> > failure. If you did it via printk() approach, it's probably wrong as my patch
> > uses internal regmap function. Most likely you need to enable trace events
> > for regmap and collect those for let's say 2 seconds:
> > 
> > 	echo 1 > ...trace events...
> > 	modprobe ...
> > 	sleep 2
> > 	echo 0 > ...trace events...
> > 
> > and dump the buffer to a file. It might have though more than needed
> > as some other devices might also use regmap at the same time. I don't remember
> > if the trace events for regmap have a device instance name field which can be
> > used as a filter.
> > 
> > Alternatively you may also try to add a printk() into regmap core, but I don't
> > think it's more practical than trace events.
> 
> Meanwhile, can you test this patch (on top of non-working case)?
> 
> diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
> index 2314744201b4..f799a7a80231 100644
> --- a/drivers/base/regmap/regmap.c
> +++ b/drivers/base/regmap/regmap.c
> @@ -1553,8 +1553,19 @@ static int _regmap_select_page(struct regmap *map, unsigned int *reg,
>  		 * virtual copy as well.
>  		 */
>  		if (page_chg &&
> -		    in_range(range->selector_reg, range->window_start, range->window_len))
> +		    in_range(range->selector_reg, range->window_start, range->window_len)) {
> +			bool bypass, cache_only;
> +
> +			bypass = map->cache_bypass;
> +			cache_only = map->cache_only;
> +			map->cache_bypass = false;
> +			map->cache_only = true;
> +
>  			_regmap_update_bits(map, sel_register, mask, val, NULL, false);
> +
> +			map->cache_bypass = bypass;
> +			map->cache_only = cache_only;
> +		}
>  	}
>  
>  	*reg = range->window_start + win_offset;
> 
> If I understood the case, the affected driver doesn't use case and we actually
> write to the selector register twice which most likely messes up the things.

Unfortunately I can not comment regarding the LT9611UXC itself, the
datasheet that I have here is pretty cryptic, incomplete and partially
written in Mandarin.

This patch though fixes an issue for me too, So:

Tested-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> # Qualcomm RB1

> But this is only a theory (since we don't have the traces yet).
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 

-- 
With best wishes
Dmitry