Re: ata_std_qc_defer not good enough for FIS-based switching ?

[Tejun Heo <htejun@gmail.com>]

Hello, Mark.

Mark Lord wrote:
>> Are there controllers which *can* handle such a mix (ahci, sil24 ?)

Yeap, sil24 can.  ahci can currently only do device based switching but 
ahci 2.0 can do it too.

>> So it looks like a I need a .qc_defer() function which examines all links
>> from the common host port for activity, and then asks for command 
>> deferral
>> when the new command has a different protocol than those that are 
>> outstanding.
>>
>> Weird that none of the other LLDs need this.  Or do they?

So, none of the others needs this.

> This seems (below) to work for sata_mv.  But I still wonder about other 
> LLDs.
> 
> 
> static int mv_qc_defer (struct ata_queued_cmd *qc)
> {
>     struct ata_link *link = qc->dev->link;
>     struct ata_port *ap = link->ap;
>     struct mv_port_priv *pp;
>     int port_is_using_ncq;
> 
>     if (ap->nr_active_links == 0)
>         return 0;
>     pp = ap->private_data;
>     port_is_using_ncq = ((pp->pp_flags & MV_PP_FLAG_NCQ_EN) != 0);
>     if (qc->tf.protocol == ATA_PROT_NCQ) {
>         if (port_is_using_ncq)
>             return ata_std_qc_defer(qc);
>     } else {
>         if (!port_is_using_ncq)
>             return sata_pmp_qc_defer_cmd_switch(qc);
>     }
>     return ATA_DEFER_LINK;
> }

Looks good to me.

Thanks.

-- 
tejun