[linux-sunxi] Re: [PATCH] ARM: sun6i: dt: Add new Mele I7 device

[Maxime Ripard]

On Tue, Mar 10, 2015 at 12:16:07PM +0100, Hans de Goede wrote:
> Hi,
> 
> On 03-03-15 14:58, Maxime Ripard wrote:
> >On Tue, Mar 03, 2015 at 02:20:31PM +0100, Hans de Goede wrote:
> >>Hi,
> >>
> >>On 03-03-15 09:22, Maxime Ripard wrote:
> >>>On Tue, Mar 03, 2015 at 08:55:36AM +0100, Hans de Goede wrote:
> >>>>>>+/ {
> >>>>>>+	model = "Mele I7 Quad top set box";
> >>>>>>+	compatible = "mele,i7", "allwinner,sun6i-a31";
> >>>>>>+
> >>>>>>+	chosen {
> >>>>>>+		bootargs = "earlyprintk console=ttyS0,115200";
> >>>>>
> >>>>>Using earlyprintk by default is a bad idea if the kernel is configured
> >>>>>with DEBUG_LL support for another SoC.
> >>>>
> >>>>While on this subject, u-boot now sets the chosen/stdout-path property
> >>>>up by default, which means that the kernel will do the right thing by
> >>>>default. So we we really do not need any bootargs= in our dts files.
> >>>
> >>>I just tested that this weekend, and it turned out that the kernel
> >>>couldn't use it so far (ie, no output until init takes over and setup
> >>>a TTY on ttyS0).
> >>>
> >>>Was it working for you?
> >>
> >>Yes, note that the kernel only honors the stdout-path property if
> >>there is no console= argument present if there is a console= argument
> >>present on the kernel cmdline then that will overrule the stdout-path
> >>property
> >
> >Yeah, I removed the bootargs entirely.
> >
> >>Which board did you test with, and what u-boot and kernel version ?
> >
> >I tested it on my A31 hummingbird, with allwinner's u-boot, but with
> >/chosen/stdout-path hardcoded to "serial0:115200n8", with a 4.0-rc1
> >kernel.
> 
> I'm not sure if stdout-path supports aliases this is what u-boot is using,
> and which works fine (with 4.0-rc1 kernel): "/soc at 01c00000/serial at 01c28000:115200"

I gave that another try, and it worked like a charm, so it really
looks like an instance of PEBKAC.

> >But it might very well just be me. We just tested it on a Marvell
> >board (that uses the same serial driver) this morning and it was fine,
> >so I don't think it's really worth worrying about this :)
> >
> >>>>Currently we've a random mix where we do have bootargs in some, but
> >>>>not in most sunxi dts files. I believe we should simply remove it
> >>>>everywhere...
> >>>
> >>>We used to set them in SoCs that are not supported by U-boot yet, and
> >>>where the bootloader won't come and patch the DT (A31, A23, A80).
> >>
> >>Ah, so that is (was) the logic, following that logic we should probably
> >>remove bootargs= from at least the a23 and a31 boards (basically
> >>from all boards but a80).
> >
> >I'm not so sure about the A31, since most boards won't even boot by
> >default on the SD card
> 
> True.
> 
> > and we have no way to replace U-Boot in NAND
> >so far (afaik). But replacing them by stdout-path is a very good
> >solution too.
> 
> You mean putting stdout-path in the dts, I'm not sure if I like that,
> to me both bootargs and stdout-path are something which should be
> left to the bootloader to set. But I understand that when not
> using upstream u-boot that may be an issue.

I know that some other platforms ask for stdout-path when they review
it, because iirc, barebox uses it to know on which console to output
its log and export its shell, which is also a valid interpretation of
that property, and, contrary to bootargs, doesn't really imply that
the bootloader should update it.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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