Re: atmel-nand-controller: NAND chip selects?

[Ladislav Michl <ladis@linux-mips.org>]

On Mon, Jun 11, 2018 at 01:21:31PM +0200, Boris Brezillon wrote:
> On Mon, 11 Jun 2018 13:04:25 +0200
> Ladislav Michl <ladis@linux-mips.org> wrote:
> 
> > Consider there are more NAND chips connected to the same lines and only nCE
> > (connected to GPIO line one per each chip) is used to select them.
> > How is driver supposed to work in such situation?
> > Common memory region cannot be requested multiple times as well as the
> > same gpio for R/B cannot be requested.
> 
> I thought you could request several times the same GPIO if it's in input
> mode, but maybe I'm wrong.

Well, it does not seem to work:
atmel-nand-controller 10000000.ebi:nand-controller: Failed to get R/B gpio (err = -16)

> > Something as davinci_nand for
> > memory region? Use 'ranges' property? How should one express in DT gpio
> > is shared between child nodes?
> 
> For both problems, the solution is to reserve the resources at the NAND
> controller level instead of the NAND level. It's pretty easy for the CS
> memory range, because the driver can easily detect when the same CS is
> used by different NAND chips. It's a bit more complicated for the R/B
> pins.

Do you mean something like this?

		ebi: ebi@10000000 {
			status = "okay";
			pinctrl-0 = <&pinctrl_nand_cs &pinctrl_nand_cs1 &pinctrl_nand_rb>;
			pinctrl-names = "default";

			nand_controller: nand-controller {
				status = "okay";
/*				reg = <0x3 0x0 0x800000>; */
				nand@3,0 {
					reg = <0x3 0x0 0x800000>;
					rb-gpios = <&pioC 13 GPIO_ACTIVE_HIGH>;
					cs-gpios = <&pioC 8 GPIO_ACTIVE_HIGH>;
					nand-bus-width = <8>;
					nand-ecc-mode = "soft";
					nand-ecc-algo = "bch";
					nand-ecc-strength = <8>;
					nand-on-flash-bbt;
					label = "atmel_nand";
				};
				nand@3,1 {
					reg = <0x3 0x0 0x800000>;
					rb-gpios = <&pioC 13 GPIO_ACTIVE_HIGH>;
					cs-gpios = <&pioC 14 GPIO_ACTIVE_HIGH>;
					nand-bus-width = <8>;
					nand-ecc-mode = "soft";
					nand-ecc-algo = "bch";
					nand-ecc-strength = <8>;
					nand-on-flash-bbt;
					label = "atmel_nand";
				};
			};
		};

Note the commented out 'reg' property. I'm not sure if you meant to actively
compare 'reg's of nand child nodes or put 'reg' property on 'nand-controller'
level (latter does not currently fly):
atmel-ebi 10000000.ebi: missing or invalid timings definition in /ahb/ebi@10000000/nand-controller
atmel-ebi 10000000.ebi: failed to configure EBI bus for /ahb/ebi@10000000/nand-controller, disabling the device

Thank you,
	ladis