Re: [PATCH 4/5 V2] ARM: tegra: paz00: add clocks required forusboperation

[Marc Dietich <marvin24-Mmb7MZpHnFY@public.gmane.org>]

Hi Stephen,

> Marc Dietrich wrote at Tuesday, August 09, 2011 1:26 PM:
> > On Tuesday 09 August 2011 20:35:45 you wrote:
> > > [...]
> > > Do you need the pll_p_out4 entry? What's that driving? Check in
> > > /sys/kernel/debug/clock/clock_tree (/sys/kernel/debug is debugfs).
> > 
> > I think it is only required to setup the correct (non-standard?)
> > frequency. Seems all other boards use 108 MHz which cause one of the
> > ports to fail. Don't ask me for details ...
> 
> ...
> 
> > root@ac100:~# cat /sys/kernel/debug/clock/clock_tree
> > 
> >    clock                          state  ref div      rate
> > 
> > --------------------------------------------------------------
> > 
> >    clk_m                          on     9            12000000
> 
> ...
> 
> >       pll_p                       on     10  x18      216000000
> 
> ...
> 
> >          pll_p_out4               on     3   9        24000000
> >          
> >             sclk                  on     2            24000000
> >             
> >                avp.sclk           off    0            24000000
> >                cop                on     1            24000000
> >                hclk               on     2   1        24000000
> >                
> >                   pclk            on     2   2        12000000
> >                   
> >                      apbdma       on     1   1        12000000
> 
> Hmm. That's pretty odd.
> 
> With the standard kernel the device ships with, what does the clock tree
> under pll_p_out4 look like? It'd be very interesting to compare that. If
> that setup is the same as what this patch sets up, the patch seems fine.

unfortunately, there is no such think in .32 kernel (the kernel deliverd with 
the device), and I don't think I can port it over.

> As far as I know all the clocks there are both unrelated to USB, and
> internal to the device, so the board shouldn't have any effect. In
> particular, avp.sclk/cop are for the internal media CPU/DSP, hclk/pclk
> are the internal AHB/APB bus clocks, and apbdma is for an internal DMA
> engine, currently only used for audio in the mainline kernel at least.

Does this mean that the internal busses you mentioned are also running at low 
speed? Would this be a hugh performance penality?

> 
> I guess I'll ask a few people internally to see if they have a clue why
> your change might be necessary.

Also take a look at seaboard, it has the same clock setting and especially 
commit dfb625f934dd40baf29ee6c43e4f130b524411a1 in the chromeos kernel:

commit dfb625f934dd40baf29ee6c43e4f130b524411a1
Author: Vincent Palatin <vpalatin-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Date:   Wed Apr 13 07:26:08 2011 -0400

    CHROMIUM: tegra: seaboard: fix ULPI transceiver clock
    
    On our seaboard-based platforms, pll_p_out4 is used to clock
    (through DAP_MCLK2) the external USB ULPI transceiver between the USB2
    port to mini-PCIe modem. And it needs to be set at 24Mhz for the
    tranceiver to work correctly.
    Revert the sclk parent to pll_c out1 (as it was before the last change)
    since it needs to stay clocked at 108MHz.
    
    Signed-off-by: Vincent Palatin <vpalatin-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
    
    BUG=chrome-os-partner:3167
    TEST=Check that the Gobi modem is appearing in lsusb listing
    Use the kaen DVT for browsing and suspending
    
    Review URL: http://codereview.chromium.org/6825076
    
    Change-Id: Ia9b1bbc7860da732fb8edbbcf0bce60e82d6d8ed


Thanks!

Marc



> For reference, here's Harmony on something roughly like linux-next:
> 
>    clk_m                          on     7            12000000
> ...
>       pll_p                       on     9   x18      216000000
> ...
>          pll_p_out4               on     2   2        108000000
>             sclk                  on     2            108000000
>                avp.sclk           off    0            108000000
>                cop                on     1            108000000
>                hclk               on     2   1        108000000
>                   pclk            on     2   2        54000000
>                      apbdma       on     1   1        54000000