From: Peter Ujfalusi <peter.ujfalusi@ti.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: <dan.j.williams@intel.com>, <dmaengine@vger.kernel.org>,
<andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH] dmaengine: dmatest: Add support for completion polling
Date: Tue, 11 Jun 2019 16:41:07 +0300 [thread overview]
Message-ID: <33c33189-1c76-fe01-5d03-6bdd877c5e4b@ti.com> (raw)
In-Reply-To: <20190611044738.GT9160@vkoul-mobl.Dlink>
On 11/06/2019 7.47, Vinod Koul wrote:
> On 10-06-19, 14:12, Peter Ujfalusi wrote:
>>> How do you know/detect transfer is completed?
>>
>> This is a bit tricky and depends on the DMA hardware.
>> For sDMA (omap-dma) we already do this by checking the channel status.
>> The channel will be switched to idle if the transfer is completed.
>
> Well we are talking about DMA and doing this kind of things doesn't make
> sense to me. Why not do memcpy/pio instead. DMA is designed to finish
> txn fast and move to next one, if we cannot do that, I would say lets
> not use dmaengine in those cases! Keeping dmaengine idle is not really
> good design.
The dra7 case is a special one: we have one errata (i878) for which the
workaround is to use something else than MCU to access DMM registers,
otherwise bus/system lockup can happen. The only feasible non MCU access
is to use DMA memcpy to read/write registers.
I've also encountered user who want to swap CPU memcpy with DMA based
one as it tends to lower the CPU load and it is faster.
- Péter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
prev parent reply other threads:[~2019-06-11 13:40 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-29 8:37 [PATCH] dmaengine: dmatest: Add support for completion polling Peter Ujfalusi
2019-05-31 6:54 ` Peter Ujfalusi
2019-06-03 7:05 ` Peter Ujfalusi
2019-06-04 12:45 ` Vinod Koul
2019-06-04 13:35 ` Peter Ujfalusi
2019-06-10 7:04 ` Vinod Koul
2019-06-10 11:12 ` Peter Ujfalusi
2019-06-11 4:47 ` Vinod Koul
2019-06-11 13:41 ` Peter Ujfalusi [this message]
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