Re: [PATCH] drivers: char: hvc: add Blackfin JTAG console support

[Mike Frysinger]

On Mon, Jan 10, 2011 at 22:41, Arnd Bergmann wrote:
> On Tuesday 11 January 2011, Mike Frysinger wrote:
>> throughput seems to be a bit lower. Âthe Blackfin JTAG hardware has
>> basically a 4 byte fifo that is filled/consumed in a single shot. Âand
>> the Blackfin can produce much faster than the host can consume. Âso
>> atm, i have it send out 4 bytes, and the hvc layers take care of
>> calling back into me at some point. Âif i add a busy loop to run a few
>> hundred milliseconds (like HZ/4), it runs much nicer. Âbut obviously
>> doesnt give anyone else time to run. Âi cant schedule or anything as
>> the write layers are called with a spin_lock_irqsave. Âany tips for
>> how to speed this up a bit ? Âor is it a wash with hvc ?
>
> You could try lowering the hvc MIN_TIMEOUT value. If you want to
> change it for blackfin, you could probably make it a configuration
> option. However, if it really takes a few milliseconds that you need
> to wait between two accesses, MIN_TIMEOUT should already be small
> enough.
>
> You should really not need to sleep in your output function, as
> the khvcd() timeout logic tries handling this in the best way.
> There may be a bug in that logic though (wouldn't be the first one
> there), so try to see what the timeouts are when you get into
> this problem.

np, i'll poke around a bit.  i'm ok with merging this driver now since
it seems to be functionality equivalent to the old code.
-mike
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