Re: [PATCH] ata: libata: preserve sata_spd link cache across ata_dev_init

[Damien Le Moal <dlemoal@kernel.org>]

On 2026/10/10 9:54, tongzhiwei wrote:
> a hot-unplug goes through
> ata_eh_schedule_probe() -> ata_dev_init() -> sata_spd = 0.
> After commit 69f2c9346313 ("ata: libata: Fix sata_down_spd_limit() when no
> link speed is reported"), when
> the device is unplugged, every probe lowers sata_spd_limit, which breaks
> commit 2dc0b46b5ea3 ("libata: sata_down_spd_limit should return if
> driver has not recorded sstatus speed"). The harm is, when the device
> is plugged back, it is limited to low speed which will never be recovered.
> 
> This patch stops zeroing sata_spd in ata_dev_init (sata_spd was
> introduced in commit 008a78961ec7 ("libata: improve SATA PHY speed down
> logic")).  sata_spd is then written only on a successful reset.  At
> struct ata_port's init time the sata_spd field is zeroed by kzalloc.
> 
> Fixes: 69f2c9346313 ("ata: libata: Fix sata_down_spd_limit() when no link speed is reported")
> Assisted-by: LLM
> Signed-off-by: tongzhiwei <tongzhiwei@cmss.chinamobile.com>
> ---
>  drivers/ata/libata-core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
> index f482c0a6d7e9..2ddad2e6ebd2 100644
> --- a/drivers/ata/libata-core.c
> +++ b/drivers/ata/libata-core.c
> @@ -5659,7 +5659,7 @@ void ata_dev_init(struct ata_device *dev)
>  
>  	/* SATA spd limit is bound to the attached device, reset together */
>  	link->sata_spd_limit = link->hw_sata_spd_limit;
> -	link->sata_spd = 0;
> +	/* link->sata_spd caches last negotiated link speed; not zeroed here */

This contradicts the previous comment, so let's make this consistent. E.g.
something like:

	/*
	 * The SATA speed limit is bound to the attached device, so reset it
	 * but keep the last negotiated speed indicated by link->sata_spd.
	 */

to replace the previous comment.

>  
>  	/* High bits of dev->flags are used to record warm plug
>  	 * requests which occur asynchronously.  Synchronize using


-- 
Damien Le Moal
Western Digital Research