Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751250AbaAEOGu (ORCPT ); Sun, 5 Jan 2014 09:06:50 -0500 Received: from moutng.kundenserver.de ([212.227.17.9]:58862 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751108AbaAEOGr (ORCPT ); Sun, 5 Jan 2014 09:06:47 -0500 From: Arnd Bergmann To: Florian Meier Subject: Re: [PATCHv9] dmaengine: Add support for BCM2835 Date: Sun, 5 Jan 2014 15:06:03 +0100 User-Agent: KMail/1.12.2 (Linux/3.8.0-22-generic; KDE/4.3.2; x86_64; ; ) Cc: "linux-arm-kernel@lists.infradead.org" , Stephen Warren , Vinod Koul , Dan Williams , "Russell King - ARM Linux" , Andy Shevchenko , devicetree , "alsa-devel@alsa-project.org" , "Lars-Peter Clausen" , "linux-kernel@vger.kernel.org" , Mark Brown , "linux-rpi-kernel" , dmaengine , Stephen Warren References: <52C5A6A3.8000405@koalo.de> <1964639.FVztRK0HBK@wuerfel> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201401051506.03481.arnd@arndb.de> X-Provags-ID: V02:K0:EGoz/t+ARYDb/HxpuSE6NmZ4Vvam0bSXmmW7F6NMzp7 DogROS64erlks4gtsuBR5TCxYsn43kffAaSK9q7g4swUiVWEUg l1OwNabpr14Cn0+GrBVFqlQNYT3yDC7DKeR/PY42HFKG2ivlBt 9EnKUdCkG5eGlrWlFiJtqCgOpSLL8+qGB4hMm1npERmZqWz4Uv /pJ9VdsCCpIhXlg9ITrfTYMvscu4/z8MW6GRKgcMEZaHZ6647x SNQDpZyqW7GowX+24yhjqxda9WA2sRbloA94RwhvUcYbKkv58i soFMAM2HHoPQopzw9Jc+ODlIr0/nRgPIMnkTxCuziYH7GDtY5m +qLd8FrGT7z2FQZCTN4Q= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Saturday 04 January 2014, Florian Meier wrote: > On 02.01.2014 19:03, Arnd Bergmann wrote: > > On Thursday 02 January 2014 18:49:23 Florian Meier wrote: > >> Add support for DMA controller of BCM2835 as used in the Raspberry Pi. > >> Currently it only supports cyclic DMA. > > > > Looks very nice. Just a few details I noticed: > > > >> +#if defined(CONFIG_OF) > >> +static const struct of_device_id bcm2835_dma_of_match[] = { > >> + { .compatible = "brcm,bcm2835-dma", }, > >> + {}, > >> +}; > >> +MODULE_DEVICE_TABLE(of, bcm2835_dma_of_match); > >> +#endif > > > > I doubt we are going to see non-DT versions of this driver, so the #ifdef > > can just get removed here. > > As already explained in previous versions of this patch thread, there is > a non-DT version in a downstream kernel and the more I make this patch > incompatible with non-DT, the harder it gets to upstream the remaining > stuff. I hope this is not something that blocks this driver from getting > accepted. In this case, that's certainly not an excuse unless you are worried about 400 bytes of .rodata in one driver and there are no side-effects of having the device ID listed when it's not used. Even if it made a real difference to another project, you'd need a much better excuse -- if you are worried about compatibility between mainline and some downstream kernel, how about changing that downstream kernel to use DT? > > [...] > > This can now be simplified using the dma_get_any_slave_channel() interface > > taht Stephen Warren introduced. > > [...] > > dma_set_mask_and_coherent() > > Sigh, the API is developing faster than I can keep track with updating > this patch. I hope some day I will be faster.... > When Russell told me about the second one before, it hoped that I can > avoid merging different trees on my own, but it seems that you want me > to do that ;-) The dma_get_any_slave_channel() change is probably my fault. I suggested both the initial dma_get_slave_channel() API and this one because the original approach turned out too complicated. If dma_set_mask_and_coherent(). I don't think you have to merge other trees, to get both APIs, they should already be part of the dma-slave tree that your patch would get merged into. If not, we can probably come up with a different solution. The dma_set_mask_and_coherent() suggestion is not as important as the dma_get_any_slave_channel() one, if you have to choose between them. > >> + if (pdev->dev.of_node) { > >> + /* Device-tree DMA controller registration */ > >> + rc = of_dma_controller_register(pdev->dev.of_node, > >> + bcm2835_dma_xlate, od); > >> + if (rc) { > >> + dev_err(&pdev->dev, "Failed to register DMA controller\n"); > >> + goto err_no_dma; > >> + } > >> + } > > > > If pdev->dev.of_node isn't set, you didn't get here, so the if() can be removed. > > Why not? (In the case of non-DT initialization) The code I quoted is right after these lines: + /* Request DMA channel mask from device tree */ + if (of_property_read_u32(pdev->dev.of_node, + "brcm,dma-channel-mask", + &chans_available)) { + dev_err(&pdev->dev, "Failed to get channel mask\n"); + rc = -EINVAL; + goto err_no_dma; + } If DT is disabled or not used, you return -EINVAL here. Arnd -- 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/