Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932891AbbFIKFt (ORCPT ); Tue, 9 Jun 2015 06:05:49 -0400 Received: from mailgw02.mediatek.com ([210.61.82.184]:52916 "EHLO mailgw02.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752240AbbFIKF1 (ORCPT ); Tue, 9 Jun 2015 06:05:27 -0400 X-Listener-Flag: 11101 Message-ID: <1433844321.16178.6.camel@mtksdaap41> Subject: Re: [PATCH 2/3] spi: mediatek: Add spi bus for Mediatek MT8173 From: Eddie Huang To: Mark Brown CC: Leilk Liu =?UTF-8?Q?=28=E5=88=98=E7=A3=8A=29?= , Mark Rutland , Matthias Brugger , Rob Herring , Pawel Moll , Ian Campbell , "Kumar Gala" , Catalin Marinas , Will Deacon , HongZhou Yang , Sascha Hauer , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-spi@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , srv_heupstream , Sascha Hauer Date: Tue, 9 Jun 2015 18:05:21 +0800 In-Reply-To: <20150608175927.GO14071@sirena.org.uk> References: <1431075343-7887-1-git-send-email-leilk.liu@mediatek.com> <1431075343-7887-3-git-send-email-leilk.liu@mediatek.com> <20150508175306.GG2761@sirena.org.uk> <1431434356.2128.9.camel@mhfsdcap03> <20150512160540.GB3066@sirena.org.uk> <1431675522.2128.13.camel@mhfsdcap03> <20150515092543.GY2761@sirena.org.uk> <1433758546.19786.16.camel@mtksdaap41> <20150608175927.GO14071@sirena.org.uk> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2799 Lines: 73 Hi Mark, On Mon, 2015-06-08 at 18:59 +0100, Mark Brown wrote: > On Mon, Jun 08, 2015 at 06:15:46PM +0800, Eddie Huang wrote: > > On Fri, 2015-05-15 at 17:25 +0800, Mark Brown wrote: > > > > That's how a very large proportion of devices that work with DMA are > > > done - why would this be complicated? All can_dma() does is report if > > > DMA is possible. > > > In include/linux/spi/spi.h, it describes if can_dma() exists and returns > > true, dma_tx and dma_rx must be set.But Medaitek SPI controller has its > > own dma hardware, which means this dma resides in the same base address > > range with SPI controller, and only used by SPI, so we don't implement > > generic DMA driver, such that can't provide dma channel and assign to > > dmx_tx, dmx_rx parameter. We think it's strange to implement generic dma > > driver for dma that only used by specific hardware.Can we just provide > > can_dma() function and return false ? But I think it's a little odd that > > there actually has dma. So can we just skip can_dma() function let it be > > NULL ? > > If it's simply the unavailbility of a struct dma_chan we must be able to > get a better solution than just open coding all the DMA mapping and > unmapping in the driver. The only thing we actually use the channel for > is to get the device we need to use to do the mapping and unmapping, > either we need a way for devices to provide their own channels easily or > a way for SPI drivers to specify a device here instead of a channel. > The latter seems easier if a bit clunky (with having to work with both). I list two ways you mention. Pesudo code of your first suggestion: static int mtk_spi_probe(struct platform_device *pdev) { struct dma_chan *tx_chan; struct dma_device *tx_dma; tx_chan = devm_kzalloc(&pdev->dev, sizeof(*tx_chan), GFP_KERNEL); tx_dma = devm_kzalloc(&pdev->dev, sizeof(*tx_dma), GFP_KERNEL); tx_dma->dev = &pdev->dev; tx_chan->device = tx_dma; master->dma_tx = tx_chan; ... } Modification of your second suggestion: --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -539,8 +539,8 @@ static int __spi_map_msg(struct spi_master *master, struct spi_message *msg) if (!master->can_dma) return 0; - tx_dev = master->dma_tx->device->dev; - rx_dev = master->dma_rx->device->dev; + tx_dev = master->dma_tx ? master->dma_tx->device->dev : master->dev; + rx_dev = master->dma_rx ? master->dma_rx->device->dev : master- Is this what you want ? Actually, I don't like first one at all. Eddie Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/