linux-kernel - Re: sunxi spi clock problem

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Date:	Sun, 22 May 2016 22:58:09 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Emilio López <emilio@...pez.com.ar>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>,
	linux-clk <linux-clk@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: sunxi spi clock problem

Hi,

On Sun, May 22, 2016 at 10:18 PM, Michal Suchanek <hramrach@...il.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.

Regards
ChenYu

>
> Thanks
>
> Michal
>
> root@...s:~/spidisp# ./spitest -r 50 -d -s 1000000 /dev/spidev2.0
> Debug mode.
> spidev spi2.0: setup mode 0, 8 bits/w, 40000000 Hz max --> 0
> spidev spi2.0: spi mode 0
> spidev spi2.0: setup mode 0, 8 bits/w, 40000000 Hz max --> 0
> spidev spi2.0: msb first
> spidev spi2.0: setup mode 0, 8 bits/w, 40000000 Hz max --> 0
> spidev spi2.0: 0 bits per word
> spidev spi2.0: setup mode 0, 8 bits/w, 1000000000 Hz max --> 0
> /dev/spidev2.0: spi mode 0x0, 8 bits per word, 1000000000 Hz maxspidev
> spi2.0: mclk spi2 (24000000)
>
> Sending 00
> spidev spi2.0: mclk spi2 setting rate 2000000000Hz
> spidev spi2.0: mclk spi2 (864000000)
> spidev spi2.0: clkdiv 0 CDR2 0 regval 4096
> spi_master spi2: spi2.0: timeout transferring 1 bytes@...0000000Hz for
> 100(100)ms
> spidev spi2.0: SPI transfer failed: -110
> spi_master spi2: failed to transfer one message from queue
> xfer: Connection timed out
> buffer size: 1, result -110
> buffer size: 1, result -110, Connection timed out
> Sending
> maximum buffer size: 0
> Using gpio 50.
> Writing gpio export 50 to /sys/class/gpio/export.
> Reading gpio direction from /sys/class/gpio/gpio50/direction: in
>
> Reading gpio inversion from /sys/class/gpio/gpio50/active_low: 0
>
> Writing gpio direction in to /sys/class/gpio/gpio50/direction.
> Reading gpio value from /sys/class/gpio/gpio50/value: 1
>
> Writing gpio direction out to /sys/class/gpio/gpio50/direction.
> Writing gpio value 0 to /sys/class/gpio/gpio50/value.
> Writing gpio value 1 to /sys/class/gpio/gpio50/value.
> Writing gpio value 0 to /sys/class/gpio/gpio50/value.
> Writing gpio value 1 to /sys/class/gpio/gpio50/value.
> Sending 9f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> spidev spi2.0: mclk spi2 (864000000)
> spidev spi2.0: mclk spi2 setting rate 2000000000Hz
> spidev spi2.0: mclk spi2 (864000000)
> spidev spi2.0: clkdiv 0 CDR2 0 regval 4096