linux-kernel - Re: [PATCH v3 01/12] gpio: rockchip: avoid division by zero

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Message-ID: <Ztcw4wVHsQkYkjhr@smile.fi.intel.com>
Date: Tue, 3 Sep 2024 18:53:07 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Ye Zhang <ye.zhang@...k-chips.com>
Cc: linus.walleij@...aro.org, brgl@...ev.pl, heiko@...ech.de,
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mika.westerberg@...ux.intel.com, tao.huang@...k-chips.com,
	finley.xiao@...k-chips.com, tim.chen@...k-chips.com,
	elaine.zhang@...k-chips.com
Subject: Re: [PATCH v3 01/12] gpio: rockchip: avoid division by zero

On Tue, Sep 03, 2024 at 03:36:38PM +0800, Ye Zhang wrote:
> If the clk_get_rate return '0', it will happen division by zero.

I don't understand the circumstances when it may happen.

> Fixes: 3bcbd1a85b68 ("gpio/rockchip: support next version gpio controller")

Not sure that this actually fixes anything. See below why I think so.

...

>  	if (bank->gpio_type == GPIO_TYPE_V2 && !IS_ERR(bank->db_clk)) {

Here you explicitly checked that the clock is provided by DT.

...

>  		freq = clk_get_rate(bank->db_clk);

Here you read the frequency which may be 0 in two cases:
1) in DT explicitly set to 0;
2) CCF is disabled.

So, wrong DTs have to be validated / fixed beforehand, correct?

But if the CCF is disabled, the db_clk is NULL. Moreover I don't see
how the db_clk may contain error pointer as you have it filtered out
at _get_bank_data(). So, maybe what you need is to have NULL check
in the conditional and explaining more in the commit message why it
is currently a problematic code?

> +		if (!freq)
> +			return -EINVAL;

-- 
With Best Regards,
Andy Shevchenko