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Message-ID: <492C1816.6020405@atmel.com>
Date: Tue, 25 Nov 2008 16:21:58 +0100
From: Nicolas Ferre <nicolas.ferre@...el.com>
To: Dan Williams <dan.j.williams@...el.com>,
"Sosnowski, Maciej" <maciej.sosnowski@...el.com>,
Haavard Skinnemoen <hskinnemoen@...el.com>
CC: Linux Kernel list <linux-kernel@...r.kernel.org>,
ARM Linux Mailing List
<linux-arm-kernel@...ts.arm.linux.org.uk>,
Andrew Victor <linux@...im.org.za>
Subject: Re: [PATCH] dmaengine: at_hdmac: new driver for the Atmel AHB DMA
Controller
Dan Williams :
> On Fri, Nov 14, 2008 at 9:34 AM, Nicolas Ferre <nicolas.ferre@...el.com> wrote:
>>>> include/linux/at_hdmac.h | 26 +
>>> ...this header should be moved somewhere under arch/arm/include.
>> This is where dw_dmac.h resides. Moreover, if one day this IP is implemented
>> on a different architecture, it will be good not to reach it through
>> arch/arm path.
>
> Ok, I won't gate acceptance on this since dw_dmac already set the
> precedent, but shouldn't the header move after the IP has been
> duplicated? Just my 2cents.
Ok, I follow your advice.
>>>> + memset(desc, 0, sizeof(struct at_desc));
>>>> + dma_async_tx_descriptor_init(&desc->txd, chan);
>>>> + async_tx_ack(&desc->txd);
>>> the DMA_CTRL_ACK bit is under control of the client. It should be
>>> read-only to the driver (except for extra descriptors that the driver
>>> creates on behalf of the client).
>> This is precisely where the descriptors are been created so, I thought it
>> should be ok to initialize this bit. Am I right ?
>>
>
> They will be acknowledged by client code. Calls like async_memcpy
> assume that the the ack bit is clear by default so they can specify
> some actions to run at completion time. By setting it early, at
> descriptor allocation time, async_tx will get confused.
This ack bit is annoying me : I cannot figure out how it is used for
plain memcopy/slave offload calls...
Moreover, at recycle time, if I keep a descriptor chain as a whole, I
have to introduce another state for my descriptors : consumed but not
freed yet (with another linked list management).
If I only take care of the ACK flag for releasing descriptors, I loose
the dependency in my descriptor chain (in a multi-descriptor memcpy case).
Can I only consider this information without taking care of the chaining
dependency (and loose this information in a multi-descriptor operation) ?
Or, may I drop this DMA_CTRL_ACK bit management as I do not have the
usefulness of redoing an operations on one descriptor (no xor engine) ?
Kind regards,
--
Nicolas Ferre
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