Re: pxa2xx_spi suspend/resume

[Daniel Ribeiro <drwyrm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Em Qui, 2009-03-12 às 23:35 -0400, Ned Forrester escreveu:
> Hmmm... This looks scary.  If the DRCMR registers went to zero, what
> else has changed in the DMA setup?  A call to pxa2xx_spi_remove() would
> have cleared these, but that should not be called for suspend/resume.
> Have you checked all the other DMA related registers that are assigned
> to the SSP device?  Are these the only ones that are anomalous, or are
> these just the first ones you found?
> 
> Actually, I don't think there are any other registers, save the ones
> that will be set up by pump_transfers(), anyway.  The PXA270 has a few
> more DMA related registers than the PXA255, but I don't see anything
> that looks like trouble, other than what you found above.

Everything else is OK. DRCMR is the only thing that gets nuked and is
not restored by pump_transfers().

> I would not jump to the conclusion (perhaps you haven't, but I don't
> have the whole picture) that we just need to restore these two
> registers.  You need to make sure that the assigned DMA channels are
> still allocated.  I wonder what process cleared these registers and what
> that might mean about the possibility that DMA channel assignments were
> purged on resume.

Currently i am restoring them to their probe() values on resume(), only
if rx_channel and tx_channel are != -1 (dma enabled). It seems to be
working fine. Im not sure if this is all that is needed, but i suspect
its enough.

And i think that its not software that is nuking DRCMR, as i said on a
previous email, i dont need to restore DRCMR if i use the "core" pm_test
mode. (the core pm_test executes the suspend/resume routines just as if
it was a normal suspend/resume, the only difference is that PXA will not
be really suspend).

There is still a chance that my bootloader is nuking these registers on
resume before giving control to kernel, i will check the bootloader code
and see if this is the case. I suspect it isn't.

> You could try a patch to restore DRCMR registers to see if that fixes
> the problem or just makes things worse.  I don't recommend submitting
> such a patch without guidance from someone more knowledgeable about DMA
> and suspend/resume.

It fixes the problem here, im not sure if its all that is needed, so,
lets wait for more comments on this before i submit the patch.

> In the process of searching for inspiration on this matter, I was
> reminded of another poster who has tried getting suspend/resume to work.
>  I don't think that the thread:

I googled the ML archives before posting and found this thread. And
altough it has the same symptoms, i think it may be a different problem.
I discarded his fix proposal at the first debug run, because my SSP
registers are exactly what i expected on resume(), and exactly the same
as they were on suspend().

-- 
Daniel Ribeiro


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