| Message ID | 1416917249.32327.15.camel@debian.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 25 Nov 2014 12:07:29 +0000 , Ian Campbell <ijc@debian.org> wrote: > On Tue, 2014-11-25 at 11:17 +0000, Leif Lindholm wrote: > > On Tue, Nov 25, 2014 at 10:35:04AM +0000, Mark Rutland wrote: > > > On Mon, Nov 24, 2014 at 10:23:58PM +0000, Leif Lindholm wrote: > > > > Support specifying console options (like with console=ttyXN,<options>) > > > > by appending them to the stdout-path property after a separating ':'. > > > > > > > > Example: > > > > stdout-path = "uart0:115200"; > > > > > > I would very much like to be able to use this -- it will allow > > > distributions to boot on a board without having to know _anything_ about > > > the console UART until userspace is up, which would make it possible to > > > have a completely generic installer image, without requiring the > > > platform to provide bootargs. > > > > > > My only concern is that this conflates the set of kernel command line > > > options for the UART wit the DT binding for it. I don't know how good > > > people are at keeping those options stable, and I know they are > > > currently not documented -- we would need to add a stdout-path options > > > section to relevant UART bindings. > > > > I don't disagree. > > > > Current options are fairly well defined and stable, at least for any > > driver that uses uart_parse_options() (documented in > > Documentation/serial/driver). > > My concern is that this is Linux specific, other OSes may have different > ideas about how stdout options should be formatted within this property. > (At least I don't know of any standardisation of the 115200n8 thing -- > I'd love to be corrected!) > > If I were a firmware author I'd be wary of specifying a stdout-path with > a Linux specific suffix. > > Search ePAPR for baud it seems that the generic serial binding includes > a current-speed property in 6.2.1.2. It then goes on a bit ambiguously > to talk about the NS16550 in 6.2.2 but I think 6.2.1.2 was intended to > be generic. No mention of stop-bits/parity etc though, they are assumed > to be set already I think > > One thought I had was to define a dt-stdout "pseudo-console" so that > console=dt-stdout,115200n8 or something could be used. > > Anyway I applied your patch to v3.18-rc5 and ran it on a Mustang and it > didn't work for some reason. I'm using: > > fdt set /chosen stdout-path "/soc/serial@1c020000:115200" > setenv bootargs "earlycon=uart8250,mmio32,0x1c020000 root=/dev/sda3 rw debug" > > So I get earlycon but then no proper console. Removing earlycon just > makes that stop working. > > With: > > diff --git a/drivers/of/base.c b/drivers/of/base.c > index 89c6b33..5dc1718 100644 > --- a/drivers/of/base.c > +++ b/drivers/of/base.c > @@ -1840,6 +1840,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) > of_stdout_options = strchr(name, ':'); > if (of_stdout_options != NULL) > of_stdout_options++; > + printk(KERN_CRIT "%s: name=%s of_stdout=%p options=%s\n", > + __func__, name, of_stdout, of_stdout_options); > } > } > > > I can see in dmesg: > [ 0.000000] of_alias_scan: name=/soc/serial@1c020000:115200 of_stdout= (null) options=115200 > > So it seems like of_find_node_by_path() is confused by the ":". That would be a bug in of_find_node_by_path(). Should add a test case for that because ':' is supposed to terminate path parsing. > I've not tried it but I'd have expected something more like: > if (name) { > of_stdout_options = strchr(name, ':'); > if (of_stdout_options != NULL) { > *of_stdout_options = '0'; > of_stdout_options++; > } > of_stdout = of_find_node_by_path(name); > } This isn't really right because it modifies the property data which is supposed to be const. of_find_node_by_path() already does the search piecewise, so it should be fairly straightforward to add a test for the ':'. Anyone care to take a look? If I need to do it then it will take a couple of weeks before I've got some free time. :-/ > > i.e. strip the options then do the patch lookup. name is const so this > won't actually work, but something like it... > > Ian. >
diff --git a/drivers/of/base.c b/drivers/of/base.c index 89c6b33..5dc1718 100644 --- a/drivers/of/base.c +++ b/drivers/of/base.c @@ -1840,6 +1840,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align)) of_stdout_options = strchr(name, ':'); if (of_stdout_options != NULL) of_stdout_options++; + printk(KERN_CRIT "%s: name=%s of_stdout=%p options=%s\n", + __func__, name, of_stdout, of_stdout_options); } }