Re: [PATCH 1/3] pata_pdc202xx_old: fix UDMA mode for Promise UDMA33 cards

[Jeff Garzik <jeff@garzik.org>]

On 02/13/2010 08:35 AM, Bartlomiej Zolnierkiewicz wrote:
> From: Bartlomiej Zolnierkiewicz<bzolnier@gmail.com>
> Subject: [PATCH] pata_pdc202xx_old: fix UDMA mode for Promise UDMA33 cards
>
> On Monday 04 January 2010 02:30:24 pm Russell King wrote:
>
>> Found the problem - getting rid of the read of the alt status register
>> after the command has been written fixes the UDMA CRC errors on write:
>>
>> @@ -676,7 +676,8 @@ void ata_sff_exec_command(struct ata_port *ap, const struct
>> ata_taskfile *tf)
>>          DPRINTK("ata%u: cmd 0x%X\n", ap->print_id, tf->command);
>>
>>          iowrite8(tf->command, ap->ioaddr.command_addr);
>> -       ata_sff_pause(ap);
>> +       ndelay(400);
>> +//     ata_sff_pause(ap);
>>   }
>>   EXPORT_SYMBOL_GPL(ata_sff_exec_command);
>>
>>
>> This rather makes sense.  The PDC20247 handles the UDMA part of the
>> protocol.  It has no way to tell the PDC20246 to wait while it suspends
>> UDMA, so that a normal register access can take place - the 246 ploughs
>> on with the register access without any regard to the state of the 247.
>>
>> If the drive immediately starts the UDMA protocol after a write to the
>> command register (as it probably will for the DMA WRITE command), then
>> we'll be accessing the taskfile in the middle of the UDMA setup, which
>> can't be good.  It's certainly a violation of the ATA specs.
>
> Fix it by adding custom ->sff_exec_command method for UDMA33 chipsets.
>
> Debugged-by: Russell King<rmk@arm.linux.org.uk>
> Signed-off-by: Bartlomiej Zolnierkiewicz<bzolnier@gmail.com>
> ---
>   drivers/ata/pata_pdc202xx_old.c |   13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)

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