On Sat, Jul 5, 2014 at 11:28 PM, Kevin Hao <haokexin@xxxxxxxxx> wrote:
> The sata on fsl mpc8315e is broken after the commit 8a4aeec8d2d6
> ("libata/ahci: accommodate tag ordered controllers"). The reason is
> that the ata controller on this SoC only implement a queue depth of
> 16. When issuing the commands in tag order, all the commands in tag
> 16 ~ 17 are mapped to tag 0 unconditionally and then causes the sata
> malfunction. It makes no senses to use a 32 queue in software while
> the hardware has less queue depth. This patch provides the function
> for libata to adjust the queue depth for a host controller.
>
> Fixes: 8a4aeec8d2d6 ("libata/ahci: accommodate tag ordered controllers")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Kevin Hao <haokexin@xxxxxxxxx>
> ---
> v2: Remove the changes for the ata tag helper functions.
>
> drivers/ata/libata-core.c | 29 ++++++++++++++++++++++++++---
> include/linux/libata.h | 3 +++
> 2 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index 8f3043165048..c9c51646d8e8 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -4728,14 +4728,14 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words)
> static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap)
> {
> struct ata_queued_cmd *qc = NULL;
> - unsigned int i, tag;
> + unsigned int i, tag, max_queue = ap->host->queue_depth;
>
> /* no command while frozen */
> if (unlikely(ap->pflags & ATA_PFLAG_FROZEN))
> return NULL;
>
> - for (i = 0; i < ATA_MAX_QUEUE; i++) {
> - tag = (i + ap->last_tag + 1) % ATA_MAX_QUEUE;
> + for (i = 0; i < max_queue; i++) {
> + tag = (i + ap->last_tag + 1) % max_queue;
This change may cause the compiler to do a full divide where
previously it could optimize to power-of-2 math with the visibility of
the ATA_MAX_QUEUE constant. How about converting
ap->host->queue_depth to ap->host->queue_depth_mask? ...then this
becomes:
tag = (i + ap->last_tag + 1) & max_queue_mask
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