From: Alexander Gordeev <a.gordeev.box@gmail.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org,
kbuild test robot <lkp@intel.com>
Subject: Re: [PATCH RFC v5 2/2] dmaengine: avalon-test: Intel Avalon-MM DMA Interface for PCIe test
Date: Thu, 14 Nov 2019 16:53:32 +0100 [thread overview]
Message-ID: <20191114155331.GA19187@AlexGordeev-DPL-IR1335> (raw)
In-Reply-To: <20191114050331.GL952516@vkoul-mobl>
On Thu, Nov 14, 2019 at 10:33:31AM +0530, Vinod Koul wrote:
> On 06-11-19, 20:22, Alexander Gordeev wrote:
> > This is a sample implementation of a driver using "avalon-dma" to
> > perform data transfers between target device memory and system memory:
> >
> > +----------+ +----------+ +----------+
> > | RAM |<-->| Avalon |<---PCIe--->| Host |
> > +----------+ +----------+ +----------+
> >
> > The target device is expected to use only Avalon-MM DMA Interface for
> > PCIe to initiate DMA transactions - without custom hardware specifics
> > to make such transfers possible.
> >
> > Unlike "dmatest" driver, the contents of DMAed data is not manipulated by
> > "avalon-test" in any way. It is basically pass-through and the the data
> > are fully dependent on the target device implementation. Thus, it is up
> > to the users to analyze received or provide meaningful transmitted data.
>
> Is this the only reason why you have not used dmatest. If so, why not
> add the feature to dmatest to optionally not check the DMAed data
> contents?
The main reason is that "dmatest" does not support DMA_SLAVE type of
transactions.
I considered adding DMA_SLAVE to "dmatest". But it would break the
current neat design and does not appear solving the issue of data
verification. Simply besause in general DMA_SLAVE case there is no
data integrity criteria easily available to the driver. I.e if the
data is a sensor image then verifying it in the driver would be
pointless.
So in case of "avalon-test" I offloaded the task of data verification
to the user. The driver itself just streams user data to/from device.
In fact, this approach is not "avalon-dma" specific and could be used
with any "dmaengine" compatible driver. Moreover, it would be quite
useful for bringing up devices in embedded systems. I.e one could
master a raw display frame in user space and DMA it via the driver -
without graphic stack involved.
The only missing functionality I could think of is using DMABUFs, but that
is very easy to add.
Actually, "avalon-test" is rather a presentation of how I tested
"avalon-dma". I understand "dmatest" is more easy to trust and I could
probably make it working with DMA_SLAVE type. But that would entail
hardware design requirements:
- DMA slave should both respond to read and write transactions;
- data read should always be the same as data written;
I have such version of hardware design, but I doubt majorify of devices
out there can honor the above requirements.
Summarizing - I would suggest not to change "dmatest" and bring in a
generalized version of "avalon-test" if you find it useful for a wider
audience.
Thanks!
> --
> ~Vinod
next prev parent reply other threads:[~2019-11-14 15:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 19:22 [PATCH v5 0/2] dmaengine: avalon: Intel Avalon-MM DMA Interface forPCIe Alexander Gordeev
2019-11-06 19:22 ` [PATCH v5 1/2] dmaengine: avalon-dma: Intel Avalon-MM DMA Interface for PCIe Alexander Gordeev
2019-11-22 5:18 ` Vinod Koul
2019-11-06 19:22 ` [PATCH RFC v5 2/2] dmaengine: avalon-test: Intel Avalon-MM DMA Interface for PCIe test Alexander Gordeev
2019-11-14 5:03 ` Vinod Koul
2019-11-14 15:53 ` Alexander Gordeev [this message]
2019-11-22 5:06 ` Vinod Koul
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