On 19-02-19, 17:49, Baolin Wang wrote: > Hi Geert, > > On Tue, 19 Feb 2019 at 17:30, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > > > Hi Baolin, > > > > On Tue, Feb 19, 2019 at 4:15 AM Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: > > > On Mon, 18 Feb 2019 at 20:23, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > On Mon, Feb 18, 2019 at 11:52 AM Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: > > > > > On Mon, 18 Feb 2019 at 18:31, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > > > > > > > > > On Tue, Feb 12, 2019 at 9:25 AM Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: > > > > > > > On Fri, 1 Feb 2019 at 19:53, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: > > > > > > > > On Thu, 31 Jan 2019 at 00:52, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > > > > > > > > On Tue, Jan 22, 2019 at 2:21 PM Baolin Wang <baolin.wang@xxxxxxxxxx> 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 <arnd@xxxxxxxx> > > > > > > > > > > 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. Are you suggesting that you have more users than channels available? I dont think it is hard to debug if channels are dynamic in nature (for example we can print channel number and you know which one are you talking about, fwiw i have worked on a such a system where we grabbed the free channel) -- ~Vinod
