Re: [patch 05/25] ata: add the SW NCQ support to sata_nv for MCP51/MCP55/MCP61

[Jeff Garzik <jeff@garzik.org>]

Kuan Luo wrote:
> hi,
> i saw the below changes  from
> http://git.kernel.org/?p=linux/kernel/git/jgarzik/libata-dev.git;a=commi
> tdiff;h=5a5a9e1890b8260686218a68862d880daee1a817
> 
> [libata] sata_nv: Clean up ATA_FLAG_NCQ usage; bit test micro-opt
> 
>  @@ -622,7 +622,9 @@ static const struct ata_port_info nv_port_info[] =
> {
>         /* SWNCQ */
>         {
>                 .sht            = &nv_swncq_sht,
> -               .flags          = ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY,
> +               .flags          = ATA_FLAG_SATA | ATA_FLAG_NO_LEGACY |
> +                                 ATA_FLAG_NCQ,
> +               .link_flags     = ATA_LFLAG_HRST_TO_RESUME,
>                 .pio_mask       = NV_PIO_MASK,
>                 .mwdma_mask     = NV_MWDMA_MASK,
>                 .udma_mask      = NV_UDMA_MASK,
> 
> If swncq_enabled is set zero by user, nv_swncq_host_init would not be
> called .
>  Then ncq should be disabled and the libata shouldn't send ncq cmd. 
>  I am not sure whether the  ATA_FLAG_NCQ flag which is in default set
> makes libata send ncq cmd even when swncq_enable is 0?
> 
> nv_init_one
> 	} else if (type == SWNCQ && swncq_enabled) {
> 		dev_printk(KERN_NOTICE, &pdev->dev, "Using SWNCQ
> mode\n");
> 		nv_swncq_host_init(host);

Thanks for watching!  Yes, that looks like a problem.

I still feel the flags usage I removed was problematic.  A better 
solution, I think, would be to do follow the ADMA example of switching 
the port_info type during early initialization:

	if (type >= CK804 && adma_enabled) {
		type = ADMA;

which in our case would result in

	if (type == SWNCQ && !swncq_enabled)
		type = GENERIC;

Or, if you prefer, we could take the opposite route, _not_ set SWNCQ in 
the pci_device_id table, and instead do something like

	if (type >= MCP65 && swncq_enabled)
		type = SWNCQ;

(MCP65 is just a pulled-out-of-thin-air example)

Regards,

	Jeff