linux-kernel - Re: [PATCH V2] mfd: syscon: Use regmap max_register_is

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Message-ID: <20240927120021.b6okbwrdpguv4hp6@spiny>
Date: Fri, 27 Sep 2024 07:00:21 -0500
From: Nishanth Menon <nm@...com>
To: Lee Jones <lee@...nel.org>
CC: Arnd Bergmann <arnd@...db.de>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Mark Brown <broonie@...nel.org>,
        Shawn Guo
	<shawnguo@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        <bcm-kernel-feedback-list@...adcom.com>,
        "Florian
 Fainelli" <florian.fainelli@...adcom.com>,
        <linux-stm32@...md-mailman.stormreply.com>,
        Alexandre Torgue
	<alexandre.torgue@...s.st.com>
Subject: Re: [PATCH V2] mfd: syscon: Use regmap max_register_is_0 as needed

On 13:47-20240903, Nishanth Menon wrote:
> syscon has always set the optional max_register configuration of
> regmap to ensure the correct checks are in place. However, a recent
> commit 0ec74ad3c157 ("regmap: rework ->max_register handling")
> introduced explicit configuration in regmap framework for register
> maps that is exactly 1 register, when max_register is pointing to a
> valid register 0. This commit solved a previous limitation of regmap
> framework.
> 
> Update syscon driver to consistent in regmap configuration for
> all sizes of syscons by using this new capability by setting
> max_register_is_0, when the max_register is valid and 0.
> 
> Signed-off-by: Nishanth Menon <nm@...com>
> ---
> 
> Based on my search
> https://gist.github.com/nmenon/d537096d041fa553565fba7577d2cd24, the
> pattern of syscon registers that may potentially be impacted by this
> patch (that are exactly 1 register wide) is probably limited, though
> this patch in itself was inspired by a buggy driver code fixed in
> https://lore.kernel.org/linux-pm/20240828131915.3198081-1-nm@ti.com/
> I have tried to Cc lists that may be interested in looking closer to
> avoid un-intended side-effects.
> 
> Changes since V1:
> * Incorporate review comments by rewording commit message and $subject
>   and dropped Fixes.
> * No functional change to the patch.
> * Expand the CC list to notify potential users.
> 
> V1: https://lore.kernel.org/all/20240828121008.3066002-1-nm@ti.com/
> 
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: linux-arm-msm@...r.kernel.org
> Cc: Bjorn Andersson <andersson@...nel.org>
> Cc: bcm-kernel-feedback-list@...adcom.com
> Cc: Florian Fainelli <florian.fainelli@...adcom.com>
> Cc: linux-stm32@...md-mailman.stormreply.com
> Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>


A gentle ping.

> 
>  drivers/mfd/syscon.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index 2ce15f60eb10..3e1d699ba934 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -108,6 +108,8 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
>  	syscon_config.reg_stride = reg_io_width;
>  	syscon_config.val_bits = reg_io_width * 8;
>  	syscon_config.max_register = resource_size(&res) - reg_io_width;
> +	if (!syscon_config.max_register)
> +		syscon_config.max_register_is_0 = true;
>  
>  	regmap = regmap_init_mmio(NULL, base, &syscon_config);
>  	kfree(syscon_config.name);
> @@ -357,6 +359,9 @@ static int syscon_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	syscon_config.max_register = resource_size(res) - 4;
> +	if (!syscon_config.max_register)
> +		syscon_config.max_register_is_0 = true;
> +
>  	if (pdata)
>  		syscon_config.name = pdata->label;
>  	syscon->regmap = devm_regmap_init_mmio(dev, base, &syscon_config);
> 
> -- 
> 2.46.0
> 
> 

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D