[meta-freescale] imx.c RXTL

[Frazer, Will]

Hi Fabio,

Thanks for the response...

On Wed, Apr 29, 2015 at 10:24 AM, Fabio Estevam <festevam at gmail.com> wrote:
> Hi Will,
>
> On Wed, Apr 29, 2015 at 9:08 AM, Frazer, Will <will.frazer at eurotech.com> wrote:
>
>> In tests I can see that with the value set as 1, under intensive 
>> serial use, CPU use goes towards about 20% (solo core). With the 
>> value set to 14 it’s closer to 2%.
>
> I think your proposal makes sense.
>
> Should we also change TXTL?
Probably.  Not looked too closely at what a sensible value should be. For now, I'm only interested in RX data. Open to suggestions ;-)

>I tested your proposal and it seems we need some logic to adjust the RXTL value.
>
>For console operation we need it to be RXTL, otherwise we miss echoing the chars.
Yes. We added a check to see if it was a console for our test - leaving it set to 1 for a console tty.

>Have you tried using DMA?
Not explicitly - just used opened it as standard serial device. I assumed any DMA logic in the driver would take care of this if needed. If it doesn't, I presume it's still an issue right? Or are you saying that this needs testing separately? I guess this is kinda where I'm coming from... is there a known reason why it is the way it is?

I ought to add that I'm testing on an old kernel  (3.0.35) so driver operation may differ w.r.t DMA. The RXTL=1 setting has been around for a while but maybe other things work slightly differently. Code looks v.similar  at an overview level.

regards,
Will