linux-kernel - Re: [RFC] dmaengine: add dma_slave_get

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <51DAD2C3.8070203@metafoo.de>
Date:	Mon, 08 Jul 2013 16:54:59 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	Dan Williams <djbw@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matt Porter <matt@...orter.com>
Subject: Re: [RFC] dmaengine: add dma_slave_get_caps api

On 07/08/2013 04:03 PM, Vinod Koul wrote:
> On Mon, Jul 08, 2013 at 04:28:29PM +0200, Lars-Peter Clausen wrote:
>> On 07/08/2013 03:40 PM, Vinod Koul wrote:
>>> On Mon, Jul 08, 2013 at 02:01:35PM +0200, Lars-Peter Clausen wrote:
>>>> On 07/08/2013 10:54 AM, Vinod Koul wrote:
>>>>> +/* struct dma_slave_caps - expose capabilities of a slave channel only
>>>>> + *
>>>>> + * @src_addr_widths: bit mask of src addr widths the channel supports
>>>>> + * @dstn_addr_widths: bit mask of dstn addr widths the channel supports
>>>>> + * @src_burst_lengths: bit mask of src slave burst lengths supported
>>>>> + * @dstn_burst_lengths: bit mask of dstn slave burst lengths supported
>>>>
>>>> I'm not sure if we need the burst_lengths fields. For one we can only
>>>> express a max burst length up 32. And usually it is fine if the dma
>>>> controller does not support the burst length requested by the slave driver,
>>>> since this only specifies the maximum and the dma controller driver can
>>>> choose a value below this limit. E.g. if the max burst length is set to 16
>>>> it is still fine if the controller only supports a burst length of 8.
>>> well how are you picking up which one to use?
>>> The idea is that you query and match that with system and client to get best
>>> throughput. If you have IP block which over generations change capablities you
>>> can runtime query and then program the channel smartly!
>>
>> The client would always request the largest burst size it can support, and
>> the dma master would then select a burst size equal or smaller to it
>> depending on what it can support.
> not really, most dmac drivers will return an error when they find a value is not
> in the supported list. And that is precisely what we would like to prevent.
> If you look at current model, it mostly program value which we know is already
> a capablity and works model.

The majority of the DMA drivers will either accept any maxburst value (which
is probably broken) or round down. The only ones which accept only a fixed
set of burst sizes seem to be mmp_pdma, mmp_tdma and sa11x0-dma.

- Lars
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/