Re: [PATCH] libata: sata_down_spd_limit should return if driver has not recorded sstatus speed

[Tejun Heo <tj@kernel.org>]

Hello, David.

On Tue, Nov 14, 2017 at 04:17:25PM -0600, David Milburn wrote:
> During hotplug, it is possible for 6Gbps link speed to
> be limited all the way down to 1.5 Gbps which may lead
> to a slower link speed when drive is re-connected.

Can you please explain the scenario with more details?

>  	/* Mask off all speeds higher than or equal to the current
> -	 * one.  Force 1.5Gbps if current SPD is not available.
> +	 * one. At this point if current SPD is not available and we
> +	 * previously recorded the link speed from the Status register,
> +	 * the driver has already masked off the highest bit so mask
> +	 * should already be set to 1 or 0. Otherwise, we should
> +	 * not force 1.5Gbps on a link where we have not previously 
> +	 * recorded speed from Status register, just return in this case.
>  	 */
>  	if (spd > 1)
>  		mask &= (1 << (spd - 1)) - 1;
>  	else
> -		mask &= 1;
> +		return -EINVAL;

I get that the current behavior might not be ideal in certain
scenarios but the above seems weird, especially given the we have
link->sata_spd for cases where we can't access the spd value.

Thanks.

-- 
tejun