Re: [PATCH] libata: warn if speed limited due to 40-wire cable (v2)

[Jeff Garzik <jeff@garzik.org>]

Robert Hancock wrote:
> Here's a revised version of my previous patch to warn the user if a
> drive's transfer rate is limited because of a 40-wire cable detection.
> This one hopefully addresses Alan's previous comments - we now do this
> at the very end of the function, and the ugly if condition has been
> cleaned up somewhat. Also, it's been inadvertently tested (it seems that
> pata_amd Nvidia cable detection is broken in current -git..)
> 
> Signed-off-by: Robert Hancock <hancockr@shaw.ca>
> 
> --- linux-2.6.20-git6/drivers/ata/libata-core.c    2007-02-11 
> 17:31:19.000000000 -0600
> +++ linux-2.6.20-git6edit/drivers/ata/libata-core.c    2007-02-13 
> 19:15:58.000000000 -0600
> @@ -3305,19 +3305,7 @@ static void ata_dev_xfermask(struct ata_
>     xfer_mask = ata_pack_xfermask(ap->pio_mask,
>                       ap->mwdma_mask, ap->udma_mask);
> 
> -    /* Apply cable rule here.  Don't apply it early because when
> -     * we handle hot plug the cable type can itself change.
> -     */
> -    if (ap->cbl == ATA_CBL_PATA40)
> -        xfer_mask &= ~(0xF8 << ATA_SHIFT_UDMA);
> -    /* Apply drive side cable rule. Unknown or 80 pin cables reported
> -     * host side are checked drive side as well. Cases where we know a
> -     * 40wire cable is used safely for 80 are not checked here.
> -     */
> -        if (ata_drive_40wire(dev->id) && (ap->cbl == ATA_CBL_PATA_UNK 
> || ap->cbl == ATA_CBL_PATA80))
> -        xfer_mask &= ~(0xF8 << ATA_SHIFT_UDMA);
> -
> -
> +    /* drive modes available */
>     xfer_mask &= ata_pack_xfermask(dev->pio_mask,
>                        dev->mwdma_mask, dev->udma_mask);
>     xfer_mask &= ata_id_xfermask(dev->id);
> @@ -3348,6 +3336,25 @@ static void ata_dev_xfermask(struct ata_
>     if (ap->ops->mode_filter)
>         xfer_mask = ap->ops->mode_filter(ap, dev, xfer_mask);
> 
> +    /* Apply cable rule here.  Don't apply it early because when
> +     * we handle hot plug the cable type can itself change.
> +     * Check this last so that we know if the transfer rate was
> +     * solely limited by the cable.
> +     * Unknown or 80 wire cables reported host side are checked
> +     * drive side as well. Cases where we know a 40wire cable
> +     * is used safely for 80 are not checked here.
> +     */
> +    if (xfer_mask & (0xF8 << ATA_SHIFT_UDMA))
> +        /* UDMA/44 or higher would be available */
> +        if((ap->cbl == ATA_CBL_PATA40) ||
> +               (ata_drive_40wire(dev->id) &&
> +             (ap->cbl == ATA_CBL_PATA_UNK ||
> +                     ap->cbl == ATA_CBL_PATA80))) {
> +                  ata_dev_printk(dev, KERN_WARNING,
> +                 "limited to UDMA/33 due to 40-wire cable\n");
> +            xfer_mask &= ~(0xF8 << ATA_SHIFT_UDMA);
> +        }

it seems broken to manipulate xfer_mask after returning from the 
driver's ->mode_filter hook.

this patch is more than just a speed-limited warning printk, afaics