linux-kernel - [FIX] [CRITICAL] Re: [PATCH] clk: divider: Fix overflow in clk_divider

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Date:	Sun, 25 May 2014 01:33:26 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Tomasz Figa <t.figa@...sung.com>,
	linux-arm-kernel@...ts.infradead.org
CC:	Mike Turquette <mturquette@...aro.org>,
	linux-kernel@...r.kernel.org,
	Maxime COQUELIN <maxime.coquelin@...com>
Subject: [FIX] [CRITICAL] Re: [PATCH] clk: divider: Fix overflow in clk_divider_bestdiv

Mike,

On 15.05.2014 18:51, Tomasz Figa wrote:
> Hi Mike,
> 
> On 07.05.2014 18:24, Tomasz Figa wrote:
>> Commit c686078 ("clk: divider: Add round to closest divider") introduced
>> a helper function to check whether given divisor is the best one instead
>> of direct check. However due to int type used instead of unsigned long
>> for passing calculated rates to this function in certain cases an
>> overflow could occur, for example when trying to obtain maximum possible
>> clock rate by calling clk_round_rate(..., UINT_MAX).
>>
>> This patch fixes this issue by changing the type of rate, now and best
>> arguments of the function to unsigned long, which is the type that
>> should be used for clock rates.
>>
>> Signed-off-by: Tomasz Figa <t.figa@...sung.com>
>> ---
>>  drivers/clk/clk-divider.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
>> index c572945..e0b360a 100644
>> --- a/drivers/clk/clk-divider.c
>> +++ b/drivers/clk/clk-divider.c
>> @@ -232,7 +232,7 @@ static int _div_round(struct clk_divider *divider, unsigned long parent_rate,
>>  }
>>  
>>  static bool _is_best_div(struct clk_divider *divider,
>> -		int rate, int now, int best)
>> +		unsigned long rate, unsigned long now, unsigned long best)
>>  {
>>  	if (divider->flags & CLK_DIVIDER_ROUND_CLOSEST)
>>  		return abs(rate - now) < abs(rate - best);
>>
> 
> Ping. It's quite important fix as the issue makes all Exynos boards
> using sdhci-s3c almost unusable.

Any issues with this patch?

Due to this issue, now since almost 3 weeks, all Samsung boards using
sdhci-s3c have been suffering from boot failures on linux-next due to
incorrect clock rates being calculated.

Best regards,
Tomasz
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