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

[Dinh Nguyen]

On 05/20/2015 07:35 PM, Krzysztof Kozlowski wrote:
> On 21.05.2015 09:16, Krzysztof Kozlowski wrote:
>> 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.
> 
> I sent a patch. Could you test on your board and confirm that this fixes
> the issue?
> 

Thanks alot for the patch! It does indeed fixes the issue for me.

Dinh

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