Re: 2.5.7 pre-UDMA PIIX bug

[Martin Dalecki <dalecki@evision-ventures.com>]

Mikael Pettersson wrote:
> Vojtech's version of drivers/ide/piix.c which went into 2.5.7
> oopses with a divide-by-zero exception when initialising older
> pre-UDMA chips, like in the following 430HX chipset:
> 
> 00:00.0 Host bridge: Intel Corporation 430HX - 82439HX TXC [Triton II] (rev 03)
> 00:07.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II] (rev 01)
> 00:07.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II]
> (PCI IDs 8086:1250, 8086:7000, and 8086:7010, respectively)
> 
> The error occurs in piix.c:piix_set_drive() line 334, shown below.
> The 82371SB has PIIX_UDMA_NONE in the piix_ide_chips[] array,
> so piix_config->flags & PIIX_UDMA is zero, which makes "umul" zero,
> which causes the divide-by-zero on line 334.
> 
>   317	static int piix_set_drive(ide_drive_t *drive, unsigned char speed)
>   318	{
>   319		ide_drive_t *peer = HWIF(drive)->drives + (~drive->dn & 1);
>   320		struct ata_timing t, p;
>   321		int err, T, UT, umul;
>   322	
>   323		if (speed != XFER_PIO_SLOW && speed != drive->current_speed)
>   324			if ((err = ide_config_drive_speed(drive, speed)))
>   325				return err;
>   326	
>   327		umul =  min((speed > XFER_UDMA_4) ? 4 : ((speed > XFER_UDMA_2) ? 2 : 1),
>   328			piix_config->flags & PIIX_UDMA);
>   329	
>   330		if (piix_config->flags & PIIX_VICTORY)
>   331			umul = 2;
>   332	
>   333		T = 1000000000 / piix_clock;
>   334		UT = T / umul;

I think that it should be just sufficient to add the
following test just in front of the offending calculartion.

if (umul == 0)
   ++umul;

Vojtech is this right?