linux-kernel - Re: [PATCH v3] dmaengine: Add basic debugfs support

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Message-ID: <970899d9-1491-78e8-1e7a-14e40915d061@ti.com>
Date:   Fri, 28 Feb 2020 12:01:34 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dan.j.williams@...el.com>, <geert@...ux-m68k.org>
Subject: Re: [PATCH v3] dmaengine: Add basic debugfs support

Hi Vinod,

On 28/02/2020 6.47, Vinod Koul wrote:
> Hi Peter,
> 
> On 26-02-20, 14:10, Peter Ujfalusi wrote:
> 
>>>  do we really want a custom dbg_show()..? Drivers can add their own
>>> files...
>>
>> They could do that already ;)
>>
>> With the custom dbg_show() DMA drivers can save on the surrounding
>> code and just fill in the information regarding to their HW.
>> Again, on am654 the default information is:
>> # cat /sys/kernel/debug/dmaengine 
>> dma0 (285c0000.dma-controller): number of channels: 96
>>
>> dma1 (31150000.dma-controller): number of channels: 267
>>  dma1chan0    | 2b00000.mcasp:tx
>>  dma1chan1    | 2b00000.mcasp:rx
>>  dma1chan2    | in-use
>>  dma1chan3    | in-use
>>  dma1chan4    | in-use
>>  dma1chan5    | in-use
>>
>> With my current .dbg_show implementation for k3-udma:
>> # cat /sys/kernel/debug/dmaengine 
>> dma0 (285c0000.dma-controller): number of channels: 96
>>
>> dma1 (31150000.dma-controller): number of channels: 267
>>  dma1chan0    | 2b00000.mcasp:tx (MEM_TO_DEV, tchan8 [0x1008 -> 0xc400], PDMA, TR mode)
>>  dma1chan1    | 2b00000.mcasp:rx (DEV_TO_MEM, rchan8 [0x4400 -> 0x9008], PDMA, TR mode)
>>  dma1chan2    | in-use (MEM_TO_MEM, chan2 pair [0x1002 -> 0x9002], PSI-L Native, TR mode)
>>  dma1chan3    | in-use (MEM_TO_MEM, chan3 pair [0x1003 -> 0x9003], PSI-L Native, TR mode)
>>  dma1chan4    | in-use (MEM_TO_MEM, chan4 pair [0x1004 -> 0x9004], PSI-L Native, TR mode)
>>  dma1chan5    | in-use (MEM_TO_MEM, chan5 pair [0x1005 -> 0x9005], PSI-L Native, TR mode)
>>
>> For me this makes a huge difference.
> 
> Ok
> 
>>>> +DEFINE_SHOW_ATTRIBUTE(dmaengine_debugfs);
>>>> +
>>>> +static int __init dmaengine_debugfs_init(void)
>>>> +{
>>>> +	/* /sys/kernel/debug/dmaengine */
>>>> +	debugfs_create_file("dmaengine", 0444, NULL, NULL,
>>>> +			    &dmaengine_debugfs_fops);
>>>
>>> Should we add a directory? That way we can keep adding stuff into that
>>> one
>>
>> and have this file as 'summary' underneath?
> 
> Correct

/sys/kernel/debug/dmaengine/summary, right?

>> I like the fact hat I can get all the information via one file.
>> Saves a lot of time (and explaining to users) on finding the correct
>> one to cat...
> 
> But am sure we can come with more data to show, so having a directory
> helps :)

OK, so we need to store the dbgfs rootdir and add an API so DMA drivers
can get the dentry of it, so they can implement their custom
files/directories underneath.

- Péter

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