Re: [PATCH] ata: libata-scsi: set the field pointer when rejecting CDL

[Niklas Cassel <cassel@kernel.org>]

Hello Shao,

On Thu, Oct 29, 2026 at 07:03:14PM +0800, shao.mingyin@zte.com.cn wrote:
> From: Shao Mingyin <shao.mingyin@zte.com.cn>
> 
> ata_mselect_control_ata_feature() rejects enabling CDL while NCQ
> priority is enabled, but unlike its other error branches it returns
> without setting *fp.
> 
> ata_scsi_mode_select_xlat() initializes fp to 0xffff and, when the
> handler fails, adds the mode select header and block descriptor lengths
> to it.  The resulting sense data then reports a field pointer far
> outside of the submitted parameter list instead of the byte that has to
> be changed.
> 
> Set *fp to the beginning of the mode page data, as the other branches of
> this function do.
> 
> Fixes: df60f9c64576 ("scsi: ata: libata: Add ATA feature control sub-page translation")
> Signed-off-by: Shao Mingyin <shao.mingyin@zte.com.cn>
> ---
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 5cde90fe594e..c07c1ff09757 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -4494,6 +4494,7 @@ static int ata_mselect_control_ata_feature(struct ata_queued_cmd *qc,
>  		if (dev->flags & ATA_DFLAG_NCQ_PRIO_ENABLED) {
>  			ata_dev_err(dev,
>  				"NCQ priority must be disabled to enable CDL\n");
> +			*fp = 0;
>  			return -EINVAL;
>  		}
>  		ata_dev_dbg(dev, "Enabling CDL\n");


Setting fp to zero looks very wrong to me, even though with the current
overly complicated code where buf and fp was using completely different
offsets, it was actually correct.

I reworked and included your patch in my series:
https://lore.kernel.org/linux-ide/20261103205448.931471-17-cassel@kernel.org/

This way we can set the fp to the logical value for anyone actually
looking at the definition of this mode page in the SAT spec.

(Where the CDL_CTRL field is at offset 4 in the ATA Feature Control mode page)


Kind regards,
Niklas