On 2020-07-22 09:18, Michal Simek wrote:
On 13. 07. 20 18:08, Maarten Brock wrote:
On 2020-07-13 14:10, Helmut Grohne wrote:
Hi Michal,
On Mon, Jul 13, 2020 at 01:49:38PM +0200, Michal Simek wrote:
On 13. 07. 20 9:11, Helmut Grohne wrote:
> Let me try to enumerate those I know:
>
> uart0 | uart1 | console | remark
> ---------+----------+---------+----------
> serial0 | serial1 | ttyPS0 | regular case
> serial0 | serial1 | ttyPS1 | normal assignment, second console
> serial1 | serial0 | ttyPS0 | -> Jan Kiszka, broken since revert
> disabled | serial0 | ttyPS0 | use only uart1 as serial0
> serial0 | disabled | ttyPS0 | regular case with uart1 disabled
>
> Out of these, I'm actively using configurations 3 and 4.
>
> Which of these scenarios do you test already?
For above we are missing also others
serial1 | serial0 | ttyPS1
disabled| serial1 | ttyPS1
Is it actually possible to have ttyPS1, but no ttyPS0? I think I
tried
doing that earlier and it resulted in there being ttyPS0, but no
ttyPS1.
What if you also have a 16550 (in the PL) and give it the serial0
alias?
Or a UARTlite? The serialN alias is inappropriate to set the number
for
ttyPSn. How are you supposed to create all of ttyPS0, ttyS0 and ttyUL0
using a single serial0 alias?
yes this combination is not possible and I don't think this is xilinx
specific issue.
I expect the same problem you have with ttyAMA, ttyS and others.
Well, it is very easy to add a 16550 in the programmable logic of a
Zynq.
Worse, it's impossible to only add uartps devices as the IP for it is
not available to the public.
It is less easy to add a 16550 to a CPU with ttyAMA but no external bus.
But if you add e.g. an I2C/SPI based SC16IS7xx which generates ttySCx
you
might have the same problems.
But the problem is worse. What happens if you give the serial0 alias to
a xilinx_uartps and the 16550 driver has already taken ttyS0? (Or vice
versa?) Will the uartps still use ttyPS0 or will it ignore the serial0
alias? I predict the latter.
I see only two ways out.
* Let uartps generate ttySx device names, or
* Do not use serialN alias to set the number.
It was already stated that it is impossible to have ttyPS1 and no
ttyPS0.
That would mean we cannot give serial0 to ttyS0 and serial1 to ttyPS1.
This makes me wonder if the opposite is valid: to give serial0 to ttyPS0
and serial1 to ttyS1. Probably not either.
There really needs to be a way to create deterministic names for the
devices!
serial1 | disables | ttyPS0
I'm not sure what this is supposed to mean. When there is no serial0
alias, I'd expect ttyPS0 to be missing. However as indicated above
that
is not what happens in practice. So either of these two
configurations
seems invalid to me.
All of these above are just not setting any console= on bootargs.
We usually set the console= assignment on bootargs.
It means mix of these combinations is tested regularly but not all
of
them. Do you see any other combination which is not supported?
I'm not aware of further relevant combinations.
Can we maybe trim down the matrix somehow? In my context, the need
for
swapping the serial aliases arises from a limitation in u-boot-xlnx
and
the desire to use one dtb for both linux and u-boot. It requires that
the serial0 alias is the console. Are there other reasons to swap
them?
If not, maybe fixing u-boot would be an option?
Helmut
I think that it would be better if u-boot used a "console" alias.
console is defined in bootargs which is OS specific feature. U-Boot has
no idea what ttyPS, ttyS, etc means. That's why I don't think there is
something wrong in this in u-boot. But please elaborate more on this
because I am not aware about any issue on u-boot configuration.
Thanks,
Michal
What I meant to say is that apparently U-boot requires serial0 to point
to
the user-interface. This limits your options when assigning aliases. If
U-boot would use a different entry (e.g. "console" or better yet
"earlycon") things might be easier. serial0 should not be special IMHO.
But let's not diverge too much here.
Maarten
