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Message-ID: <CACh+v5Mi2Qd58SZkwW0mZ3ZJx3Rv3mwSkRqzgHwBTxpUbwjVFQ@mail.gmail.com> Date: Thu, 28 Apr 2016 14:18:25 +0200 From: Jean-Jacques Hiblot <jjhiblot@...phandler.com> To: Boris Brezillon <boris.brezillon@...e-electrons.com> Cc: Jean-Jacques Hiblot <jjhiblot@...phandler.com>, Mark Rutland <mark.rutland@....com>, devicetree <devicetree@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>, Pawel Moll <pawel.moll@....com>, Ian Campbell <ijc+devicetree@...lion.org.uk>, Nicolas Ferre <nicolas.ferre@...el.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>, Alexandre Belloni <alexandre.belloni@...e-electrons.com>, Kumar Gala <galak@...eaurora.org>, Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [PATCH v6 2/2] memory: atmel-ebi: add DT bindings documentation 2016-04-28 10:49 GMT+02:00 Boris Brezillon <boris.brezillon@...e-electrons.com>: > Hi Jean-Jacques, > > On Thu, 28 Apr 2016 10:32:49 +0200 > Jean-Jacques Hiblot <jjhiblot@...phandler.com> wrote: > >> Hi Boris, >> >> i haven't seen this code in a while :) I'm glad you're working on it >> >> 2016-04-27 16:35 GMT+02:00 Boris Brezillon <boris.brezillon@...e-electrons.com>: >> > The EBI (External Bus Interface) is used to access external peripherals >> > (NOR, SRAM, NAND, and other specific devices like ethernet controllers). >> > Each device is assigned a CS line and an address range and can have its >> > own configuration (timings, access mode, bus width, ...). >> > This driver provides a generic DT binding to configure a device according >> > to its requirements. >> > For specific device controllers (like the NAND one) the SMC timings >> > should be configured by the controller driver through the matrix and smc >> > syscon regmaps. >> > >> > Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com> >> > --- >> > .../bindings/memory-controllers/atmel,ebi.txt | 146 +++++++++++++++++++++ >> > 1 file changed, 146 insertions(+) >> > create mode 100644 Documentation/devicetree/bindings/memory-controllers/atmel,ebi.txt >> > >> > diff --git a/Documentation/devicetree/bindings/memory-controllers/atmel,ebi.txt b/Documentation/devicetree/bindings/memory-controllers/atmel,ebi.txt >> > new file mode 100644 >> > index 0000000..0f332d2 >> > --- /dev/null >> > +++ b/Documentation/devicetree/bindings/memory-controllers/atmel,ebi.txt >> > @@ -0,0 +1,146 @@ >> > +* Device tree bindings for Atmel EBI >> > + >> > +The External Bus Interface (EBI) controller is a bus where you can connect >> > +asynchronous (NAND, NOR, SRAM, ....) and synchronous memories (SDR/DDR SDRAMs). >> > +The EBI provides a glue-less interface to asynchronous memories though the SMC >> > +(Static Memory Controller). >> > +Synchronous memories (and some asynchronous memories like NANDs) can be >> > +attached to specialized controllers which are responsible for configuring the >> > +bus appropriately according to the connected device. >> > +In the other hand, the bus interface can be automated for simple asynchronous >> > +devices. >> > + >> > +Required properties: >> > + >> > +- compatible: "atmel,at91sam9260-ebi" >> > + "atmel,at91sam9261-ebi" >> > + "atmel,at91sam9263-ebi0" >> > + "atmel,at91sam9263-ebi1" >> > + "atmel,at91sam9rl-ebi" >> > + "atmel,at91sam9g45-ebi" >> > + "atmel,at91sam9x5-ebi" >> > + "atmel,sama5d3-ebi" >> > + >> > +- reg: Contains offset/length value for EBI memory mapping. >> > + This property might contain several entries if the EBI >> > + memory range is not contiguous >> > + >> > +- #address-cells: Must be 2. >> > + The first cell encodes the CS. >> > + The second cell encode the offset into the CS memory >> > + range. >> > + >> > +- #size-cells: Must be set to 1. >> > + >> > +- ranges: Encodes CS to memory region association. >> > + >> > +- clocks: Clock feeding the EBI controller. >> > + See clock-bindings.txt >> > + >> > +Child chip-select (cs) nodes contain the memory devices nodes connected to >> > +such as NOR (e.g. cfi-flash) and NAND. >> > +There might be board specific devices like FPGAs. >> > +You'll define you device requirements in these child nodes. >> > + >> > +Required child cs node properties: >> > + >> > +- #address-cells: Must be 2. >> > + >> > +- #size-cells: Must be 1. >> > + >> > +- ranges: Empty property indicating that child nodes can inherit >> > + memory layout. >> > + >> > +Optional child cs node properties: >> > +- atmel,bus-width: width of the asynchronous device's data bus >> > + 8, 16 or 32. >> > + 8 if not present. >> > + >> > +- atmel,byte-access-type "write" or "select" (see Atmel datasheet). >> > + "select" if not present. >> > + >> > +- atmel,read-mode "nrd" or "ncs". >> > + "ncs" is not present. >> > + >> > +- atmel,write-mode "nwe" or "ncs". >> > + "ncs" is not present. >> > + >> > +- atmel,exnw-mode "disabled", "frozen" or "ready". >> > + "disabled" if not present. >> > + >> > +- atmel,page-mode enable page mode if present. The provided value >> > + defines the page size (supported values: 4, 8, >> > + 16 and 32). >> > + >> > +Optional device timings expressed in nanoseconds (if the property is not >> > +present 0 is assumed): >> >> IMO If no timing information is provided, it's probably better not to >> change it. It may have been configured by the bootloader or romboot. >> It may not be the perfect timings but at least it could work, whereas >> filling up with 0 is most probably going to break the access: it's a >> kind of very agressive timing optimization > > Yes, probably. I'll make all those timings mandatory in the next > version. > >> >> > + >> > +- atmel,ncs-rd-setup-ns >> > +- atmel,nrd-setup-ns >> > +- atmel,ncs-wr-setup-ns >> > +- atmel,nwe-setup-ns >> > +- atmel,ncs-rd-pulse-ns >> > +- atmel,nrd-pulse-ns >> > +- atmel,ncs-wr-pulse-ns >> > +- atmel,nwe-pulse-ns >> > +- atmel,nwe-cycle-ns >> > +- atmel,nrd-cycle-ns >> > +- atmel,tdf-ns >> >> One thought about the configuration in 'ns' unit: Some devices may >> have requirements expressed in clock cycles (I'm thinking of FPGA >> here). At a fixed frequency one can always convert manually from 'ns' >> to 'clocks' but it's a bit tedious and prone to rounding errors. And >> It 'll break when the EBI frequency is changed > > If you don't mind, I'd like to first get this version accepted, and > we'll extend it with timings expressed in clock cycles afterward. > > BTW, could you describe a real use case where timings should be > expressed in clock cycles? I mean, usually the devices have some timing > constraints (tXX_min = Y ns), and I don't see why it would differ for > FPGA interfaces, but I'm clearly not an FPGA expert. I'm not either, I only toyed with FPGA. That's just what experienced FPGA designer told me. I guess that it boils down to: FPGA are more suited for a synchronous design than an asynchronous one. JJ > > Thanks, > > Boris > > -- > Boris Brezillon, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@...ts.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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