Re: [PATCH] dmaengine: pl300: enable the clock to PL330 dma

[Dinh Nguyen]

Hi Krzysztof,

On 05/05/2015 02:22 PM, Dinh Nguyen wrote:
> On 05/05/2015 09:56 AM, Dinh Nguyen wrote:
>> On 05/04/2015 10:55 PM, Krzysztof Kozlowski wrote:
>>> 2015-05-05 4:52 GMT+09:00 Dinh Nguyen <dinguyen@xxxxxxxxxxxxxxxxxxxxx>:
>>>> On 05/04/2015 09:06 AM, Dinh Nguyen wrote:
>>>>> +CC Olof
>>>>>
>>>>> On 5/4/15 8:50 AM, Krzysztof Kozlowski wrote:
>>>>>> 2015-05-04 22:28 GMT+09:00 Dinh Nguyen <dinguyen@xxxxxxxxxxxxxxxxxxxxx>:
>>>>>>> Hi Krzystof,
>>>>>>>
>>>>>>> On 5/4/15 12:30 AM, Krzysztof Kozlowski wrote:
>>>>>>>> 2015-05-04 13:28 GMT+09:00  <dinguyen@xxxxxxxxxxxxxxxxxxxxx>:
>>>>>>>>> From: Dinh Nguyen <dinguyen@xxxxxxxxxxxxxxxxxxxxx>
>>>>>>>>>
>>>>>>>>> Turn on the clock to the PL330 DMA if there is a clock node provided.
>>>>>>>>
>>>>>>>> Why? There is no explanation in the patch for this important question - why?
>>>>>>>>
>>>>>>>> Amba bus already does this and provide a wrapper function.
>>>>>>>> Additionally that would mess up with runtime PM and clock
>>>>>>>> enable/disable.
>>>>>>>
>>>>>>> I don't see the clock for the DMA getting turned on at all, which is why
>>>>>>> after the kernel has booted, the filesystem tries to open up a serial
>>>>>>> port using DMA and the system hangs. The failure is seen here:
>>>>>>>
>>>>>>> http://arm-soc.lixom.net/bootlogs/next/next-20150504/socfpga-arm-multi_v7_defconfig.html
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>> The amba bus and pl330 should enable the clock and then disable it
>>>>>> after probing:
>>>>>> static int amba_probe(struct device *dev)
>>>>>> {
>>>>>> ...
>>>>>>         ret = amba_get_enable_pclk(pcdev);
>>>>>> ...
>>>>>>
>>>>>> I wonder why do you think it is not enabled at all?
>>>>>
>>>>> I've checked it down to the register level that the gate for this clock
>>>>> does not get set.
>>>>>
>>>>>>
>>>>>>>
>>>>>>> This only happens with the multi_v7_defconfig, because the PL330 DMA is
>>>>>>> getting built into the kernel, while the socfpga_defconfig does not
>>>>>>> enable the PL330.
>>>>>>
>>>>>> It makes sense. If pl330 driver is not enabled then necessary clocks
>>>>>> are turned on by bootloader. Probing pl330 effectively disables the
>>>>>> clock (if DMA is not used).
>>>>>>
>>>>>>> The DTS for the socfpga platform looks like this:
>>>>>>>
>>>>>>> pdma: pdma@ffe01000 {
>>>>>>>         compatible = "arm,pl330", "arm,primecell";
>>>>>>>         reg = <0xffe01000 0x1000>;
>>>>>>>         interrupts = <0 104 4>,
>>>>>>>                     <0 105 4>,
>>>>>>>                 ...
>>>>>>>                 #dma-cells = <1>;
>>>>>>>                 #dma-channels = <8>;
>>>>>>>                 #dma-requests = <32>;
>>>>>>>                 clocks = <&l4_main_clk>;
>>>>>>>                 clock-names = "apb_pclk";
>>>>>>> };
>>>>>>>
>>>>>>> Perhaps I have the wrong designation for clock-names and the amba bus is
>>>>>>> not able to pick up the correct clock?
>>>>>>
>>>>>> I have two ideas:
>>>>>> 1. Is this really the clock for the DMA? If DMA is not used then
>>>>>> disabling it should be OK.
>>>>>
>>>>> Yes, this is the clock for the DMA. Yeah, leaving this clock off is
>>>>> fine, until the DMA gets used. Up until v4.0, SoCFPGA was not using the
>>>>> DMA at all, but in v4.0, there was a patch to assign the UARTs to it's
>>>>> DMA channel.
>>>>>
>>>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/arch/arm/boot/dts/socfpga.dtsi?id=78c03c7af89721bd8a4428408a8cc7b53972e4b8
>>>>>
>>>>>> 2. Disabling the clock may effectively disable its parent or
>>>>>> grandparent if there are not more users. Maybe some other driver needs
>>>>>> these parents to be enabled? This was the issue for at least one
>>>>>> similar error (on Exynos boards).
>>>>>>
>>>>>
>>>>> I'll check up on these issues. When I was debugging this issue, the
>>>>> l4_main_clk is only used by the DMA, so it was not getting turned on by
>>>>> an other drivers.
>>>>>
>>>>
>>>> Ah, it looks like perhaps there's a problem with the serial driver and
>>>> suspend/resume? If disable CONFIG_PM, then the DMA seems to be working
>>>> fine with the debug uart. It appears the DMA is getting suspended and
>>>> doesn't get resumed.
>>>>
>>>
>>> You mean runtime PM suspend and resume or system sleep? During boot
>>> only the first one should happen.
>>
>> It's runtime PM suspend/resume.
>>
>>>
>>> Could you test the DMA with dmatest? Disable the DMA in UART and
>>> compile with CONFIG_DMATEST. Syntax for testing is here:
>>> Documentation/dmaengine/dmatest.txt
>>>
>>
>> # echo Y > /sys/module/dmatest/parameters/run
>> [   93.143775] dmatest: Started 1 threads using dma0chan0
>> [   93.149227] pm_generic_runtime_resume
>> [   93.153334] dmatest: Started 1 threads using dma0chan1
>> [   93.159380] dmatest: Started 1 threads using dma0chan2
>> [   93.165041] dmatest: Started 1 threads using dma0chan3
>> [   93.170280] dmatest: Started 1 threads using dma0chan4
>> [   93.175996] dmatest: Started 1 threads using dma0chan5
>> [   93.181642] dmatest: Started 1 threads using dma0chan6
>> [   93.188754] dmatest: dma0chan1-copy0: summary 10 tests, 0 failures
>> 282 iops 2008 KB/s (0)
>> [   93.197091] dmatest: Started 1 threads using dma0chan7
>> [   93.199353] dmatest: dma0chan3-copy0: summary 10 tests, 0 failures
>> 297 iops 2260 KB/s (0)
>> [   93.205407] dmatest: dma0chan0-copy0: summary 10 tests, 0 failures
>> 177 iops 1364 KB/s (0)
>> [   93.215599] dmatest: dma0chan2-copy0: summary 10 tests, 0 failures
>> 196 iops 1450 KB/s (0)
>> [   93.219994] dmatest: dma0chan4-copy0: summary 10 tests, 0 failures
>> 225 iops 1554 KB/s (0)
>> [   93.224322] dmatest: dma0chan5-copy0: summary 10 tests, 0 failures
>> 231 iops 1948 KB/s (0)
>> [   93.230065] dmatest: dma0chan6-copy0: summary 10 tests, 0 failures
>> 231 iops 1759 KB/s (0)
>> [   93.231251] dmatest: dma0chan7-copy0: summary 10 tests, 0 failures
>> 298 iops 2331 KB/s (0)
>> [   93.243523] pm_generic_runtime_suspend
>> root@socfpga_cyclone5:~#
>>
> 
> If I run dmatest the 2nd time it fails. It does not look like
> amba_pm_runtime_resume() is getting called to turn on the clocks on the
> subsequent tries.
> 


I managed to track this down the call dmaengine_terminate_all(), which
then calls into pl330_terminate_all(). So in pl330_terminate_all(), it
call _stop, which hits a infinite loop, UNTIL. But since the
amba_pm_runtime_resume() has not been called yet, the clock is turned
off. Thus, we're stuck in an infinite loop.

I'm not sure what would be right approach to fix this?

Thanks,

Dinh

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