Re: [PATCH] libata: clear TF before IDENTIFYing

[Mark Lord <liml@rtr.ca>]

Tejun Heo wrote:
> Some devices chock if Feature is not clear when IDENTIFY is issued.
> Set ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE for IDENTIFY such that whole
> TF is cleared when reading ID data.
> 
> Kudos to Art Haas for testing various futile patches over several
> months and Mark Lord for pointing out the fix.
> 
> Signed-off-by: Tejun Heo <htejun@gmail.com>
> Cc: Art Haas <ahaas@airmail.net>
> Cc: Mark Lord <mlord@pobox.com>

Signed-off-by: Mark Lord <mlord@pobox.com>

> I think this should go into -stable but a little bit hesitant because
> the code hasn't been tested widely.  This patch should really be
> harmless but who knows.  Jeff, Mark, what do you think?

If it was up to me, I'd plunk it directly into 2.6.20.1 and earlier.
But Jeff has his own ways..

 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 667acd2..d6fcf0a 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -1478,7 +1478,16 @@ int ata_dev_read_id(struct ata_device *dev, 
> unsigned int *p_class,
>     }
> 
>     tf.protocol = ATA_PROT_PIO;
> -    tf.flags |= ATA_TFLAG_POLLING; /* for polling presence detection */
> +
> +    /* Some devices choke if TF registers contain garbage.  Make
> +     * sure those are properly initialized.
> +     */
> +    tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
> +
> +    /* Device presence detection is unreliable on some
> +     * controllers.  Always poll IDENTIFY if available.
> +     */
> +    tf.flags |= ATA_TFLAG_POLLING;
> 
>     err_mask = ata_exec_internal(dev, &tf, NULL, DMA_FROM_DEVICE,
>                      id, sizeof(id[0]) * ATA_ID_WORDS);
> -
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