Re: [PATCHv5 1/3] dts: socfpga: Add bindings for Altera SoC SDRAM controller

[Alan Tull]

On Tue, May 27, 2014 at 2:42 PM, Steffen Trumtrar
<s.trumtrar@xxxxxxxxxxxxxx> wrote:
> On Tue, May 27, 2014 at 02:12:17PM -0500, Alan Tull wrote:
>> On Tue, May 27, 2014 at 2:11 AM, Steffen Trumtrar
>> <s.trumtrar@xxxxxxxxxxxxxx> wrote:
>> > On Wed, May 21, 2014 at 10:38:34AM -0500, Thor Thayer wrote:
>> >> On Tue, May 20, 2014 at 9:44 AM, Steffen Trumtrar
>> >> <s.trumtrar@xxxxxxxxxxxxxx> wrote:
>> >> > Hi!
>> >> >
>> >> > On Tue, May 20, 2014 at 09:31:06AM -0500, Alan Tull wrote:
>> >> >> On Mon, May 19, 2014 at 2:37 PM, Thor Thayer <tthayer.linux@xxxxxxxxx> wrote:
>> >> >>
>> >> >> >>> >> diff --git a/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt b/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt
>> >> >> >>> >> new file mode 100644
>> >> >> >>> >> index 0000000..8f8746b
>> >> >> >>> >> --- /dev/null
>> >> >> >>> >> +++ b/Documentation/devicetree/bindings/arm/altera/socfpga-sdram.txt
>> >> >> >>> >> @@ -0,0 +1,11 @@
>> >> >> >>> >> +Altera SOCFPGA SDRAM Controller
>> >> >> >>> >> +
>> >> >> >>> >> +Required properties:
>> >> >> >>> >> +- compatible : "altr,sdr-ctl";
>> >> >> >>> >> +- reg : Should contain 1 register ranges(address and length)
>> >> >> >>> >> +
>> >> >> >>> >> +Example:
>> >> >> >>> >> +     sdrctl@ffc25000 {
>> >> >> >>> >> +             compatible = "altr,sdr-ctl";
>> >> >> >>> >> +             reg = <0xffc25000 0x1000>;
>> >> >> >>> >> +     };
>> >> >> >>> >> diff --git a/arch/arm/boot/dts/socfpga.dtsi b/arch/arm/boot/dts/socfpga.dtsi
>> >> >> >>> >> index df43702..6ce912e 100644
>> >> >> >>> >> --- a/arch/arm/boot/dts/socfpga.dtsi
>> >> >> >>> >> +++ b/arch/arm/boot/dts/socfpga.dtsi
>> >> >> >>> >> @@ -676,6 +676,11 @@
>> >> >> >>> >>                       clocks = <&l4_sp_clk>;
>> >> >> >>> >>               };
>> >> >> >>> >>
>> >> >> >>> >> +             sdrctl@ffc25000 {
>> >> >> >>> >> +                     compatible = "altr,sdr-ctl", "syscon";
>> >> >> >>> >                                                    ^^^^^^^^^^
>> >> >> >>> >
>> >> >> >>> > Get rid of that, too, please.
>> >> >> >>>
>> >> >> >>> Hi Steffan,
>> >> >> >>>
>> >> >> >>> I believe I need to keep the "syscon". The same register (ctrlcfg)
>> >> >> >>> that has the ECC enable bitfield also includes the DRAM configuration
>> >> >> >>> bitfields that other drivers will want to access (specifically the
>> >> >> >>> FPGA bridge needs this information). Since this register will be
>> >> >> >>> shared between drivers,  syscon seems like the best solution.
>> >> >> >>>
>> >> >> >>
>> >> >> >> Hm, from looking at the documentation of the ctrlcfg I can't really
>> >> >> >> understand which bits you would need for the FPGA brigde and why.
>> >> >>
>> >> >> Hi Steffen,
>> >> >>
>> >> >> Offset 0x80 in the sdr-ctl is the "fpgaportrst" register.  14 bits
>> >> >> wide, defaults to 0.  When appropriate bits set to 1 in that reg, it
>> >> >> allows an FPGA port to come out of reset (enables that port).  Has no
>> >> >> other effect on SDRAM configuration.
>> >> >>
>> >> >> >> That all sounds like stuff you would want to set for the specific
>> >> >> >> RAM you are dealing with on a specific board.
>> >> >> >> What bridge are you talking about? The SDRAM bridge?
>> >> >>
>> >> >> Yes, the port allows the FPGA a direct path to the SDRAM.  This one
>> >> >> register the only register in the sdr that the bridge driver needs.
>> >> >>
>> >> >
>> >> > So, what I suggested down ...
>> >> >
>> >> >> >>
>> >> >> >> I can see the problem with the ECC enable, though.
>> >> >> >>
>> >> >> >> Regards,
>> >> >> >> Steffen
>> >> >> >>
>> >> >> >
>> >> >> >>> >                 sdrctl@ffc25000 {
>> >> >> >>> >                         compatible = "altr,sdr-ctl";
>> >> >> >>> >                         reg = <0xffc25000 0x1000>;
>> >> >> >>> >                         ranges;
>> >> >> >>> >
>> >> >> >>> >                         edac@ffc2502c {
>> >> >> >>> >                                 compatible = "altr,sdram-edac";
>> >> >> >>> >                                 reg = <0xffc2502c 0x50>;
>> >> >> >>> >                                 interrupts = <0 39 4>;
>> >> >> >>> >                         };
>> >> >> >>> >                 };
>> >> >> >>> >
>> >> >> >>> > Then we can later add:
>> >> >> >>> >
>> >> >> >>> >                         sdr-ports: ports@ffc2507c {
>> >> >> >>> >                                 #reset-cells = <1>;
>> >> >> >>> >                                 compatible = "altr,sdr-ports";
>> >> >> >>> >                                 reg = <0xffc2507c 0x10>;
>> >> >> >>> >                                 clocks = <&ddr_dqs_clk>;
>> >> >> >>> >                                 ...
>> >> >> >>> >                         };
>> >> >>
>> >> >
>> >> > ... here should work. No?! Just a simple driver that registers with the
>> >> > reset-framework. I would add 0x7c to that driver and than that driver could
>> >> > "configure" the port and let it out of reset.
>> >> >
>> >> > I have done the same thing for the other 3 bridges, but am not finished yet.
>> >> > Especially the GPV-stuff needs to at least be able to be added later if not now.
>> >> >
>> >
>> > Hi Thor!
>> >
>> >> I'm not clear on how the EDAC driver will interact with the registers
>> >> allocated to the SDRAM controller. If the group of registers from
>> >> 0xffc25000 to 0xffc26000 is exclusively allocated to the SDRAM
>> >> controller, how does the EDAC driver cleanly access that single
>> >> register inside this range?
>> >>
>> >
>> > The compatible in the example is wrong. I didn't mean to map the whole address space
>> > to some driver.
>> > I think for the configuration register syscon is the right approach. It is a
>> > bag of bits that don't necessitate an own driver, so syscon is perfect.
>> >
>> > So, let me change my proposal to
>> >
>> >         sdr-ctl: sdram@ffc25000 {
>> >                 compatible = "altr,sdr-ctl", "syscon";
>> >                 reg = <0xffc25000 0x1>;
>> >         };
>> >
>> >         edac: edac@ffc2502c {
>> >                 compatible = "altr,sdram-edac";
>> >                 reg = <0xffc2502c 0x50>;
>> >                 interrupts = <0 39 4>;
>> >                 config = <&sdr-ctl>;
>> >                 ...
>> >         };
>> >
>> >         sdr-ports: ports@ffc2507c {
>> >                 compatible = "altr,sdr-ports";
>> >                 reg = <0xffc2507c 0x10>;
>> >                 clocks = <&ddr_dqs_clk>;
>> >                 ...
>> >         };
>> >
>> > Maybe we can just skip the outer node that combines all the others.
>> > So, if we do it like that, you can still use syscon, but only for the register
>> > that needs it. And the EDAC definitely needs access to the config register, so
>> > all is good.
>> >
>> >> Is the solution that I don't use request_region() (and therefore not
>> >> request exclusive access) when setting up the SDRAM controller?
>> >>
>> >> If you could point me to your drivers for the other bridges that you
>> >> reference, your code may answer my question.
>> >>
>> >
>> > The other bridges don't need access to any SDRAM controller registers and
>> > I haven't even started to implement the GPV-stuff with the lw2hps-bridge :-(
>> >
>> > Regards,
>> > Steffen
>> >
>> > --
>> > Pengutronix e.K.                           |                             |
>> > Industrial Linux Solutions                 | http://www.pengutronix.de/  |
>> > Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
>> > Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
>>
>> OK now I understand.  For register offset 0x0, that's all stuff set up
>> in the bootloader.  We won't be touching that register except for the
>> EDAC.  So syscon isn't needed here.
>>
>> Each driver that uses some sdr registers can specify which registers
>> it uses in the device tree.  So far we don't have any cases of two
>> drivers that share a register.
>>
>> The ECC driver will need two ranges: offset 0x00 and 0x38 through 0x50.
>> The fpga bridges just needs offset 0x80.
>>
>
> Well, almost ;-)
> Use syscon for 0x0 and reference that in the ECC driver, which only is
> responsible for 0x38 to 0x50. Then flip the two EDAC bits via the syscon-phandle.
> Then a bootloader can probe with the same dts and have a driver match on the
> config-register and one for all the DRAM setup (< 0x38), which we don't need in
> the kernel. On the other hand the EDAC seems unneccessary for the bootloader.
> And this all matches the partitioning of the SDR register space, so I think it
> is also a correct hardware description.
>
> Regards,
> Steffen
>
> --
> Pengutronix e.K.                           |                             |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

We could do that.  But is syscon a concept the bootloader will know about?

Actually it is a bit messier than what I originally said:
 ECC driver needs two ranges: offset 0x00 and 0x38 through 0x50.
 Machine layer needs control of 0x10, 0x14, 0x54, and 0x58 for putting
SDRAM into self-refresh.
 fpga bridges needs offset 0x80.

Alan
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