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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ceFCSGNoNWqq4YNDYdMfd0R6+0aefkkTFSwlzn3bDMc=; b=YjPnXxkEHHVs8l1p8MGW2H/ZqSHRXjI236TO0amLWjVSsCCs4048SswmBxWmLbJm+N +5E/qfwShedcaOOrKtdDE5d1GXiwvU7Nl2O9rZ0AgIQ5J6DWZZBVU8nZi+4vLYrBdBPj 8N/4NN1RxLfG+01YTriKMTm+T3RRZucfz1cvdAWIc56BtYGTPRckByzH0DdJ7yIejnuN BozIoBm5HpyB2AmUMHJkgcPe55K9jr6lXiWw/gKl7kUr9fNGCqFP9GHq8q3odQFQyaqC vh7l81/eet2+sKisPMoz6diTxFCx8rsqxEOm8X5O1+4epchUu0mZYpHU4KOdkThr0ruX QN4A== X-Gm-Message-State: AHQUAuaPogkKHK5zYqChVapLgvpYJY1YjlZFg8zTQCMgNUMRaN3H0wK4 SY8VvQkxhDfGOa08Q90AwOFBtEkRz/G/9ZTDP6X5yA== X-Google-Smtp-Source: AHgI3IYsae3AMyaa7jkN8e9h6ArVPBkR535/IDlsxe3Uwr0X0LXfFZ6l+PcQHAeYndpX5oPVjC1VymuTR5sD0VSszj0= X-Received: by 2002:a2e:251:: with SMTP id 78mr11030225ljc.90.1550569770704; Tue, 19 Feb 2019 01:49:30 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Baolin Wang Date: Tue, 19 Feb 2019 17:49:19 +0800 Message-ID: Subject: Re: [PATCH 1/3] dt-bindings: dmaengine: Add one new cell to present hardware slave id To: Geert Uytterhoeven X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190219_014933_416785_E289F57E X-CRM114-Status: GOOD ( 33.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , DTML , eric.long@unisoc.com, arm-soc , Arnd Bergmann , Lyra Zhang , Mark Brown , Linux Kernel Mailing List , dmaengine@vger.kernel.org, Vinod Koul , Rob Herring , Olof Johansson , Orson Zhai , Dan Williams , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Geert, On Tue, 19 Feb 2019 at 17:30, Geert Uytterhoeven wrote: > > Hi Baolin, > > On Tue, Feb 19, 2019 at 4:15 AM Baolin Wang wrote: > > On Mon, 18 Feb 2019 at 20:23, Arnd Bergmann wrote: > > > On Mon, Feb 18, 2019 at 11:52 AM Baolin Wang wrote: > > > > On Mon, 18 Feb 2019 at 18:31, Arnd Bergmann wrote: > > > > > > > > > > On Tue, Feb 12, 2019 at 9:25 AM Baolin Wang wrote: > > > > > > On Fri, 1 Feb 2019 at 19:53, Baolin Wang wrote: > > > > > > > On Thu, 31 Jan 2019 at 00:52, Arnd Bergmann wrote: > > > > > > > > On Tue, Jan 22, 2019 at 2:21 PM Baolin Wang wrote: > > > > > > > > > > > > > > > > > > Client: > > > > > > > > > DMA clients connected to the Spreadtrum DMA controller must use the format > > > > > > > > > -described in the dma.txt file, using a two-cell specifier for each channel. > > > > > > > > > -The two cells in order are: > > > > > > > > > +described in the dma.txt file, using a three-cell specifier for each channel. > > > > > > > > > +The three cells in order are: > > > > > > > > > 1. A phandle pointing to the DMA controller. > > > > > > > > > 2. The channel id. > > > > > > > > > +3. The hardware slave id which is used for clients to trigger DMA engine > > > > > > > > > +automatically. > > > > > > > > > > > > > > > > I notice that this is an incompatible binding change. Is that necessary? > > > > > > > > If the current code works, I'd suggest allowing both #dma-cells=<2> > > > > > > > > and <3>, and then implementing both in the driver. > > > > > > > > > > > > > > Yes, this is necessary. > > > > > > > > > > > > > > Yes, current code can work, but the problem is that the DMA clients > > > > > > > must add one property (something like "sprd,slave-id") to specify the > > > > > > > slave id. So considering this, we want to change the dma-cells to 2, > > > > > > > including dma channel and dma slave id, which can avoid introducing > > > > > > > some similar properties for DMA clients. > > > > > > > > > > > > > > Now there are no DMA clients in mainline for Spreadtrum platform, and > > > > > > > we want to upstream our first DMA clients: SPI controller. So no other > > > > > > > drivers need to change when we changing dma cells. Thanks. > > > > > > > > > > > > Do you have any other concerns about this patch set? If not, I think > > > > > > Vinod can apply this patch set. Thanks. > > > > > > > > > > Sorry for the late reply. Yes, this makes sense since there are no > > > > > existing users then. For the DT changes going through the dmaengine > > > > > tree > > > > > > > > > > Acked-by: Arnd Bergmann > > > > > > > > Thanks for your reviewing. > > > > > > > > > > > > > > One more question, to make sure we don't need to edit it again: > > > > > Why do you need both a 'channel id' and a 'slave id' here? Is this > > > > > a strict hardware requirement for your DMA engine? In many > > > > > other designs, only a DMA request line number needs to > > > > > be described, and I think this would correspond to what you > > > > > call the 'hardware slave id' in your documentation. > > > > > > > > I try to explain why we need the slave id. > > > > > > > > For our DMA engine driver, we have software request mode and hardware > > > > request mode. For software request mode, the DMA engine driver need > > > > trigger DMA to start transfer manually. But for hardware request mode, > > > > we just set one unique slave id corresponding to the slave hardware to > > > > the DMA engine, then the slave hardware can trigger DMA automatically. > > > > And the slave id is not always same with the channel id according to > > > > the SoC design, so we add one cell to specify the slave id. > > > > > > I did understand the need for a slave-id, I was instead wondering about > > > the channel-id number. On many SoCs, all channels are equal, and you > > > just have to pick one of those with the right capabilities for a particular > > > slave. > > > > Yes, all channels are equal. We just set a unique slave id for the > > channel for a particular slave. For example, the SPI slave can use > > channel 10 for tx transfer by setting slave id 11, or it also can use > > channel 9 for tx transfer by setting same slave id 11. > > So the channel selection is software policy, not hardware description, and > thus doesn't belong in DT? > > Can't the DMA engine driver allocate channels dynamically, removing the > need to specify this in DT? In theory we can do as you suggested. But we still want to manage/assign the DMA channel resources manually for one SoC, we can make sure some important DMA slaves (such as audio) can request a DMA channel at runtime firstly, another benefit is that it is easy to debug since we can easily know which channel is assigned for this slave. -- Baolin Wang Best Regards _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel