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From: Rameshwar Sahu <rsahu@apm.com>
To: Vinod Koul <vinod.koul@intel.com>
Cc: dan.j.williams@intel.com, dmaengine@vger.kernel.org,
	Arnd Bergmann <arnd@arndb.de>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, jcm@redhat.com,
	patches@apm.com, Loc Ho <lho@apm.com>
Subject: Re: [PATCH v7 1/3] dmaengine: Add support for APM X-Gene SoC DMA engine driver
Date: Tue, 17 Mar 2015 15:03:14 +0530	[thread overview]
Message-ID: <CAFd313zJHP2PbN=Xa48GRmyQ6EvH=3wrZPBngtsZ2djo4ka96A@mail.gmail.com> (raw)
In-Reply-To: <CAFd313xG4EZdoS4vMxq4TW7v+xc_OEd3uC1R4LW3=Xs3+JzY9w@mail.gmail.com>

Hi Vinod,

On Mon, Mar 16, 2015 at 11:01 PM, Rameshwar Sahu <rsahu@apm.com> wrote:
> Hi Vinod,
>
> On Mon, Mar 16, 2015 at 9:56 PM, Vinod Koul <vinod.koul@intel.com> wrote:
>> On Mon, Mar 16, 2015 at 05:24:34PM +0530, Rameshwar Sahu wrote:
>>> >> >> +static void xgene_dma_free_desc_list_reverse(struct xgene_dma_chan *chan,
>>> >> >> +                                          struct list_head *list)
>>> >> > do we really care about free order?
>>> >>
>>> >> Yes it start dellocation of descriptor by tail.
>>> > and why by tail is not clear.
>>> We can free allocated descriptor in forward order from head or in
>>> reverse order, I just followed here fsldma.c driver.
>>> Does this make sense ??
>> No, you have two APIs to free list. Why do you need two?
>
> Yes, basically we have tow API to free list.
> xgene_dma_free_desc_list_reverse will call if any failure in
> allocation of memory from DMA pool in prep routines.
> Like e.g. in prep routing we have some descriptors allocated and still
> need to get descriptor to complete the DMA request and failure happen,
> so we need to free all allocated descriptor.
>
>>
>>>
>>>
>>> >
>>> >> > where are you mapping dma buffers?
>>> >>
>>> >>  I didn't get you here. Can you please explain me here what you mean.
>>> >> As per my understanding client should map the dma buffer and give the
>>> >> physical address and size to this callback prep routines.
>>> > not for memcpy, that is true for slave transfers
>>> >
>>> > For mempcy the idea is that drivers will do buffer mapping
>>>
>>> Still I am clear here, why memcpy will do buffer mapping, I see other
>>> drivers and also async_memcpy.c , they only map it and pass mapped
>>> physical dma address to driver.
>>>
>>> Buffer mapping mean you here is dma_map_xxx ?? Am I correct.
>> Yes
>
> I have confusion here, I don't see any driver dma buffer mapping in
> prep_dma_memcpy.
> Can you please clear me here if driver does this on behalf of client,
> like any example so that I can proceed further.

Any comment here ??

>>
>>>
>>> >
>>> >> > why are you calling this here, status check shouldnt do this...
>>> >>
>>> >> Okay, I will remove it.
>>> >>
>>> >>
>>> >> >> +                     spin_unlock_bh(&chan->lock);
>>> >> >> +                     return DMA_IN_PROGRESS;
>>> >> > residue here is size of transacation.
>>> >>
>>> >> We can't calculate here residue size. We don't have any controller
>>> >> register which will tell about remaining transaction size.
>>> > Okay if you cant calculate residue why do we have this fn?
>>>
>>> So basically case here for me is completion of dma descriptor
>>> submitted to hw is not same as order of submission to hw.
>>> So scenario coming in multithread running :e.g. let's assume we have
>>> submitted two descriptors first has cookie 1001 and second has 1002,
>>> now 1002 is completed first, so updated last_completed_cookie as 1002
>>> but not yer checked for dma_tx_status, and then first cookie completes
>>> and update last_completed_cookie as 1001, now second transaction check
>>> for tx_status and it get DMA_IN_PROGRESS, because
>>> last_completed_cookie(1001) is less than second transaction's
>>> cookie(1002).
>>>
>>> Due to this issue I am traversing that transaction in pending list and
>>> running list, if not there means we are done.
>>>
>>> Does this make sense??
>> That only convinces me that there is something not so correct.
>>
>> To help me understand pls let me know if below is fine:
>> - for a physical channel, do you submit multiple transactions?
>
> Yes
>
>> - if yes, how does DMA deal with multiple transactions, how does it schedule
>>   them?
>
> So , basically we submit multiple descriptor to dma physical channel,
> and dma engine execute it one by one and give us completion callback.
> So in this way we expect callback on same order as submission order
> and it does also, no issue.
>
> But problem is with supporting p+q offload, here we have P
> functionality supports in dma physical channel 0 and Q functionality
> supports in dma physical channel 1. So for pq we need to submit two
> descriptor, one to channel 0 and second to channel1, in this case we
> can't expect the completion order, because channnel 0 can finish P
> before Q or vice versa, and we need to wait to complete both before
> calling client callback() and completing cookie.
> Second thing we submit memcpy and sg on same channel, and can complete
> before even though if it submitted after PQ.

So our SoC dma engine hw design idea was to get more throughput while
running two channel concurrent and calculating the P and Q together,
but somehow now today we came to scenario where running P and Q on
different channel causing hang to dmaengine, some hw bug, So now I am
going to support P and Q generation in same channel, so above
mentioned cookie status scenario will never come.
I will send you the patch for review.

Thanks,
>
>>
>> --
>> ~Vinod
>> --
>> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

  reply	other threads:[~2015-03-17  9:33 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-12 11:15 [PATCH v7 0/3] dmaengine: APM X-Gene SoC DMA engine driver support Rameshwar Prasad Sahu
2015-03-12 11:15 ` [PATCH v7 1/3] dmaengine: Add support for APM X-Gene SoC DMA engine driver Rameshwar Prasad Sahu
2015-03-16  9:27   ` Vinod Koul
2015-03-16 10:30     ` Rameshwar Sahu
2015-03-16 11:27       ` Vinod Koul
2015-03-16 11:54         ` Rameshwar Sahu
2015-03-16 16:26           ` Vinod Koul
2015-03-16 17:31             ` Rameshwar Sahu
2015-03-17  9:33               ` Rameshwar Sahu [this message]
2015-03-17 10:19                 ` Vinod Koul
2015-03-17 10:38                   ` Rameshwar Sahu
2015-03-16 11:02     ` Rameshwar Sahu
2015-03-12 11:15 ` [PATCH v7 2/3] arm64: dts: Add APM X-Gene DMA device and DMA clock DTS nodes Rameshwar Prasad Sahu
2015-03-12 11:15 ` [PATCH v7 3/3] Documentation: dma: Add APM X-Gene SoC DMA engine driver documentation Rameshwar Prasad Sahu
2015-03-16  9:29   ` Vinod Koul
2015-03-16 10:31     ` Rameshwar Sahu

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