Re: libata bridge limits

[Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>]

> a) Why was this limit put in there? It limits both transfer speed and
>    request size. If it's due to some dodgy drive/bridge, perhaps we
>    should just check for that and only apply the transfer limits when
>    detected (or blacklisted). On the bridge setups I've seen, I've never
>    had problems with killing the limit.

Various old bridges need it - and you can't detect the bridge type.

> 
> b) Put in a whitelist, easy to do for these Mtron drives.
> 
> c) Add a parameter to turn it on (or off, depending on the default) for
>    a specific drive.
> 
> I'm in favor of a) personally, but I'd like to hear why the check was
> added originally first. Dropping 20-30% of the throughput performance on
> the floor without option seems like a really bad choice.

Can I suggest 

d) Assume the bridge is ok but teach the SATA error handling code that if
there is a timeout immediately with such a bridge then to flip down to
UDMA5 and knobble the transfer length.
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