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

[Krzysztof Kozlowski]

On 21.05.2015 05:30, Dinh Nguyen wrote:
> 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?

Good catch. I confirmed that device is not runtime resumed. I wonder why
it works in my case (pl330 on Exynos4412)...

Anyway I have an idea to fix it. I'll send a patch.

Best regards,
Krzysztof

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