From mboxrd@z Thu Jan 1 00:00:00 1970 From: geomatsi Subject: Re: DMA support for CF Date: Tue, 18 Dec 2012 21:59:44 +0000 Message-ID: <50D0E750.6070406@gmail.com> References: <50D0264C.1010907@norik.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-la0-f43.google.com ([209.85.215.43]:44011 "EHLO mail-la0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751096Ab2LRSad (ORCPT ); Tue, 18 Dec 2012 13:30:33 -0500 Received: by mail-la0-f43.google.com with SMTP id z14so854427lag.16 for ; Tue, 18 Dec 2012 10:30:31 -0800 (PST) In-Reply-To: <50D0264C.1010907@norik.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Matej Kupljen Cc: Jeff Garzik , nicolas.ferre@atmel.com, linux-ide@vger.kernel.org On 12/18/2012 08:16 AM, Matej Kupljen wrote: > Dear Sergey and Jeff, > I have a board based on AT91SAM9263, with the CF connected to > the EBI0 and I am using the pata-at91.c driver. > > My question is, can I use DMA (MWDMA and/or UDMA) for the CF card, > of course, if I add support to the driver? > Basically, the question is, can we use the HDMAC (DMA controller) > to support the DMA transfers? > Please note that the DMARQ and DMACK are connected from CF to SoC. > > > I've been looking for this in the documentation, and I cannot find the > answer. Considering that the SAM9263 is considered legacy, I have > checked the documentation for AT91SAM9R/RL and AT91SAM9G and I couldn't > find the answer there either. > > Can you answer this question, please? > If not, to whom I should send it? > > Thank you and Best Regards, > Matej Kupljen Hi, In the future could you please consider sending your questions to a proper kernel mail list cc-ing authors/maintainers if necessary. As you noted, driver pata-at91 does not have dma support. This is because originally it has been developed for a board based on at91sam9260 chip which has no dma engine. More recent at91 chips (including at91sam9263) do have dma engines. It should be possible to add dma support to pata-at91 driver and use dma transfers for CF. A couple of notes regarding at91sam9263: 1. DMA driver IIRC at91sam9263 chip has a different dma engine than all the other chips of at91 family. More recent chips have HDMAC: drivers/dma/at_hdmac.c while at91sam9263 has DWDMA: drivers/dma/dw_dmac.c 2. Size of dma transfers IIRC there is a problem with dma engine on at91sam9263 chip: it has significantly reduced block size for transfers. This leads into a fairly small max transfer size in a single block transfer. As a result, it might not be practical to use this particular dma engine for CF. Thanks, Sergey