linux-kernel - Re: Using regmap_update_bits to update a write only register

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Message-ID: <54F9E597.2050301@metafoo.de>
Date:	Fri, 06 Mar 2015 18:36:23 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Daniel Baluta <daniel.baluta@...il.com>
CC:	Mark Brown <broonie@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Using regmap_update_bits to update a write only register

On 03/06/2015 06:26 PM, Daniel Baluta wrote:
[...]
> I can reproduce the problem with:
>
> static struct reg_default xxx_reg_defaults[] = {
>          { XXX_REG_CTRL0,  0x00 },
>          { XXX_REG_CTRL1,  0x00 },
>          { XXX_REG_STATUS, 0x00 },
> };
>
> but, not if the reg default definition is:
>
> static struct reg_default xxx_reg_defaults[] = {
>          { XXX_REG_STATUS, 0x00 },
>          { XXX_REG_CTRL0,  0x00 },
>          { XXX_REG_CTRL1,  0x00 },
>    };
>
> Is this normal?

That's a rhetorical question, right?

It might be that there is a bug when growing a rbblock to the left. It 
probably went unnoticed because everybody has their reg defaults ordered in 
ascending order.

Try to put a few debug printks into regcache_rbtree_write() and 
regcache_rbtree_insert_to_block() to see what exactly is going on when a new 
register is inserted into the block. How do base_reg and top_reg change.

- Lars
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