2016-07-25 15:27 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: > On Mon, Jul 25, 2016 at 03:20:44PM +0200, Mirza Krak wrote: >> 2016-07-25 13:36 GMT+02:00 Thierry Reding <thierry.reding@xxxxxxxxx>: >> > On Thu, Jul 21, 2016 at 11:26:09AM +0100, Jon Hunter wrote: >> >> >> >> On 20/07/16 20:28, Mirza Krak wrote: >> >> > 2016-07-20 14:44 GMT+02:00 Rob Herring <robh@xxxxxxxxxx>: >> >> >> On Tue, Jul 19, 2016 at 03:36:34PM +0200, Mirza Krak wrote: >> >> >>> From: Mirza Krak <mirza.krak@xxxxxxxxx> >> >> >>> >> >> >>> Document the devicetree bindings for NOR bus driver found on Tegra20 and >> >> >>> Tegra30 SOCs >> >> >>> >> >> >>> Signed-off-by: Mirza Krak <mirza.krak@xxxxxxxxx> >> >> >>> --- >> >> >>> .../devicetree/bindings/bus/nvidia,tegra20-nor.txt | 73 ++++++++++++++++++++++ >> >> >>> 1 file changed, 73 insertions(+) >> >> >>> create mode 100644 Documentation/devicetree/bindings/bus/nvidia,tegra20-nor.txt >> >> >>> >> >> >>> diff --git a/Documentation/devicetree/bindings/bus/nvidia,tegra20-nor.txt b/Documentation/devicetree/bindings/bus/nvidia,tegra20-nor.txt >> >> >>> new file mode 100644 >> >> >>> index 0000000..9ee4a66 >> >> >>> --- /dev/null >> >> >>> +++ b/Documentation/devicetree/bindings/bus/nvidia,tegra20-nor.txt >> >> >>> @@ -0,0 +1,73 @@ >> >> >>> +Device tree bindings for NVIDIA Tegra20/30 NOR Bus >> >> >>> + >> >> >>> +The NOR controller supports a number of memory types, including synchronous NOR, >> >> >>> +asynchronous NOR, and other flash memories with similar interfaces, such as >> >> >>> +MuxOneNAND. One could also connect high speed devices like FPGAs, DSPs, >> >> >>> +CAN chips, Wi-Fi chips etc. >> >> >>> + >> >> >>> +The actual devices are instantiated from the child nodes of a NOR node. >> >> >>> + >> >> >>> +Required properties: >> >> >>> + >> >> >>> + - compatible: should be "nvidia,tegra20-nor", "nvidia,tegra30-nor" >> >> >>> + - reg: Should contain NOR controller registers location and length. >> >> >>> + - clocks: Must contain one entry, for the module clock. >> >> >>> + See ../clocks/clock-bindings.txt for details. >> >> >>> + - resets : Must contain an entry for each entry in reset-names. >> >> >>> + See ../reset/reset.txt for details. >> >> >>> + - reset-names : Must include the following entries: >> >> >>> + - nor >> >> >>> + - #address-cells: Must be set to 2 to allow memory address translation >> >> >>> + - #size-cells: Must be set to 1 to allow CS address passing >> >> >>> + - ranges: Must be set up to reflect the memory layout with four integer >> >> >>> + values for each chip-select line in use. >> >> >>> + - nvidia,config: This property represents the SNOR_CONFIG_0 register. >> >> >>> + >> >> >>> +Note that the NOR controller does not have any internal chip-select address >> >> >>> +decoding and if you want to access multiple devices external chip-select >> >> >>> +decoding must be provided. >> >> >> >> >> >> Then what are the 2 chip selects in ranges? >> >> >> >> >> >> Rob >> >> > >> >> > Those two chip selects are actually a representation of a external >> >> > decoding logic based on what we use on our board. Even though it the >> >> > NOR controller only supports one single chip select I wanted to give >> >> > an example on how one could create more chip-selects with an external >> >> > logic and what it would look like in the device tree representation. >> >> >> >> Technically, the GMI/SNOR controller supports 8 chip-selects, however, >> >> unlike some devices, it appears that software has to select the active >> >> chip-select. Although this sounds odd, I believe that the idea is that >> >> in order to support devices greater than 256MB (external address space >> >> for available NOR/async devices) you can use the chip-selects to page >> >> through memory greater than this 256MB range. At least that it my >> >> (limited) understanding! >> > >> > Actually I had assumed that software would at some point need to select >> > the active chip to switch between multiple connected chips. I suppose it >> > could be possible to have multiple chips share the same chip-select and >> > decode the address lines to determine whether they're being accessed or >> > not. >> > >> > What I don't understand, and it's further complicated by the fact that >> > external chip-selects are being used, is how does the controller get >> > told what chip to select? It seems to me like it would always access the >> > same chips because the SNOR_CONFIG_0 register is only ever written on >> > ->probe(). >> > >> > For external chip selects, how do they tie in with all this? Who gets to >> > implement this logic? Wouldn't we need to abstract this away somehow so >> > that we can support whatever board designers will come up with? >> > >> > Thierry >> >> You answered it your self :). >> >> >I suppose it >> > could be possible to have multiple chips share the same chip-select and >> > decode the address lines to determine whether they're being accessed or >> > not. >> >> That is what we do and is what I refer to as external chip-selects. > > Okay, so there aren't actually chips or pins that serve as external chip > selects, but rather the GMI address lines are used to select the chip? I > guess that's more like traditional address decoding rather than chip > select. Anyway, understanding how your board design works helps devising > a device tree binding that is flexible enough to support production > devices. > > Thierry This is the most accurate descriptor. > GMI address lines are used to select the chip Best Regards Mirza -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
