ata: pata_pdc2027x: fix division by zero in pdc_adjust_pll

[PATCH] ata: pata_pdc2027x: fix division by zero in pdc_adjust_pll

Posted by Yang Zi 1 month ago

pdc_adjust_pll() divides pout_required by pll_clock_khz before checking
that pll_clock_khz is within the valid range. If the PLL input clock is
less than 1000 Hz, pll_clock_khz is 0 and the division triggers a
divide-by-zero error.

Move the sanity check ahead of the division so the invalid input is
rejected before the ratio is computed.

Signed-off-by: Yang Zi <2959243019@qq.com>
---
diff --git a/drivers/ata/pata_pdc2027x.c b/drivers/ata/pata_pdc2027x.c
index d1d1cfb22e27..c4cff4eafbe8 100644
--- a/drivers/ata/pata_pdc2027x.c
+++ b/drivers/ata/pata_pdc2027x.c
@@ -517,7 +517,7 @@ static void pdc_adjust_pll(struct ata_host *host, long pll_clock, unsigned int b
     u16 pll_ctl;
     long pll_clock_khz = pll_clock / 1000;
     long pout_required = board_idx? PDC_133_MHZ:PDC_100_MHZ;
-    long ratio = pout_required / pll_clock_khz;
+    long ratio;
     int F, R;
 
     /* Sanity check */
@@ -527,6 +527,8 @@ static void pdc_adjust_pll(struct ata_host *host, long pll_clock, unsigned int b
         return;
     }
 
+    ratio = pout_required / pll_clock_khz;
+
     dev_dbg(host->dev, "pout_required is %ld\n", pout_required);
 
     /* Show the current clock value of PLL control register

Re: [PATCH] ata: pata_pdc2027x: fix division by zero in pdc_adjust_pll

Posted by Damien Le Moal 1 month ago

On 8/25/26 17:32, Yang Zi wrote:
> pdc_adjust_pll() divides pout_required by pll_clock_khz before checking
> that pll_clock_khz is within the valid range. If the PLL input clock is
> less than 1000 Hz, pll_clock_khz is 0 and the division triggers a
> divide-by-zero error.
> 
> Move the sanity check ahead of the division so the invalid input is
> rejected before the ratio is computed.
> 
> Signed-off-by: Yang Zi <2959243019@qq.com>

This is needs a fixes tag I think.

Other than that, looks OK.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH] ata: pata_pdc2027x: fix division by zero in pdc_adjust_pll

Posted by Niklas Cassel 3 weeks, 6 days ago

On Fri, Aug 28, 2026 at 02:48:06PM +0900, Damien Le Moal wrote:
> On 8/25/26 17:32, Yang Zi wrote:
> > pdc_adjust_pll() divides pout_required by pll_clock_khz before checking
> > that pll_clock_khz is within the valid range. If the PLL input clock is
> > less than 1000 Hz, pll_clock_khz is 0 and the division triggers a
> > divide-by-zero error.
> > 
> > Move the sanity check ahead of the division so the invalid input is
> > rejected before the ratio is computed.
> > 
> > Signed-off-by: Yang Zi <2959243019@qq.com>
> 
> This is needs a fixes tag I think.
> 
> Other than that, looks OK.
> 
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Hello Yang,

Please send a V2 with a Fixes tag.


Kind regards,
Niklas