sunxi spi clock problem

[Michal Suchanek]

Hello,

The debugfs output shows that spi2 is reparented under pll5 and the
pll5 frequency remains unchanged.

The request to get a 2GHz clock for spi is fulfilled on best-effort
basis by giving the 864MHz pll5 clock which should theoretically
result in 432MHz SPI clock.

On 22 May 2016 at 16:58, Chen-Yu Tsai <wens at csie.org> wrote:
> Hi,
>
> On Sun, May 22, 2016 at 10:18 PM, Michal Suchanek <hramrach at gmail.com> wrote:
>> Hello,
>>
>> I tried running a spidev test program on linux 4.6 and I uncovered a
>> problem with the sunxi clk framework.
>>
>> Basically the system would lock up after running the test program.
>>
>> Digging deeper I found that it locks up with commit
>> [47284e3e0f3c427c93f8583549b6c938e8a18015] spi: sun4i: allow transfers
>> to set transmission speed
>>
>> This exposes a problem with the test program. I try to set the SPI
>> sped to 1MHz but at other place the speed is multiplied by 1000 to
>> save typing zeros so the actual requested speed is 1GHz. This commit
>> probably allows that request to propagate leading to the observed
>> system lockup.
>>
>> Given the parents OSC24M, pll6 and pll5 one of pll6 and pll5 is
>> probably set up at 2GHz (or both in turn because due to some rounding
>> neither goes fully up to 2GHz resulting in 864000000 SPI clock). Then
>> the system locks up.
>
> IIRC the mod clock does not propagate rate changes up the tree.
> But some output from the debugfs would be helpful. See below.
>
>>
>> I can limit the speed in the SPI driver which is rated at 100MHz in
>> SoC manual (giving 200MHz pll) but the clk driver should probably
>> limit the clock setting to sane speeds itself.
>>
>> I am not familiar with the sunxi-clk code and it has unfortunately no
>> debug prints which would show what is programmed to what speed.
>
> You can use /sys/kernel/debug/clk/clk_summary, provided you have
> debugfs built in and mounted.

root at a10s:~/spidisp# ./spitest -d -s 1000000 /dev/spidev2.0
Debug mode.
/dev/spidev2.0: spi mode 0x0, 8 bits per word, 1000000000 Hz max
Sending 00
   clock                         enable_cnt  prepare_cnt        rate
accuracy   phase
----------------------------------------------------------------------------------------
 osc32k                                   0            0       32768
       0 0
 osc24M                                   6            6    24000000
       0 0
    ir0                                   0            0    24000000
       0 0
    spi2                                  0            0    24000000
       0 0
    spi1                                  0            0    24000000
       0 0
    spi0                                  0            0    24000000
       0 0
...
spi_master spi2: spi2.0: timeout transferring 1 bytes at 1000000000Hz for
100(100)ms
spidev spi2.0: SPI transfer failed: -110
spi_master spi2: failed to transfer one message from queue
...
    pll5                                  1            1   864000000
       0 0
       pll5_other                         0            0   864000000
       0 0
       pll5_ddr                           1            1   432000000
       0 0
...
xfer: Connection timed out
buffer size: 1, result -110
buffer size: 1, result -110, Connection timed out
Sending
   clock                         enable_cnt  prepare_cnt        rate
accuracy   phase
----------------------------------------------------------------------------------------
 osc32k                                   0            0       32768
       0 0
 osc24M                                   6            6    24000000
       0 0
    ir0                                   0            0    24000000
       0 0
    spi1                                  0            0    24000000
       0 0
    spi0                                  0            0    24000000
       0 0
    ss                                    0            0    24000000
       0 0
...
    pll5                                  1            1   864000000
       0 0
       pll5_other                         0            0   864000000
       0 0
          spi2                            0            0   864000000
       0 0
       pll5_ddr                           1            1   432000000
       0 0
...
maximum buffer size: 0
Sending 9f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
...
    pll5                                  1            1   864000000
       0 0
       pll5_other                         0            0   864000000
       0 0
          spi2                            0            0   864000000
       0 0
       pll5_ddr                           1            1   432000000
       0 0
    pll4                                  0            0   384000000
       0 0
    pll2-prediv                           0

The system locks up here before finishing the output from debugfs and
actually starting the transfer printed above.

Thanks

Michal

---

The diff between the two full outputs shows only spi2 changed:

--- clk1.txt    2016-05-22 18:38:24.890906037 +0200
+++ clk2.txt    2016-05-22 18:38:15.891003130 +0200
@@ -3,7 +3,6 @@
  osc32k                                   0            0       32768
        0 0
  osc24M                                   6            6    24000000
        0 0
     ir0                                   0            0    24000000
        0 0
-    spi2                                  0            0    24000000
        0 0
     spi1                                  0            0    24000000
        0 0
     spi0                                  0            0    24000000
        0 0
     ss                                    0            0    24000000
        0 0
@@ -69,6 +68,7 @@
        pll6_sata                          0            0   100000000
        0 0
     pll5                                  1            1   864000000
        0 0
        pll5_other                         0            0   864000000
        0 0
+          spi2                            0            0   864000000
        0 0
        pll5_ddr                           1            1   432000000
        0 0
     pll4                                  0            0   384000000
        0 0
     pll2-prediv                           0            0     1500000
        0 0