On 7/23/19 7:21 PM, Jan Kiszka wrote:
> On 23.07.19 18:38, Ralf Ramsauer wrote:
>>
>>
>> On 7/23/19 5:35 PM, Jan Kiszka wrote:
>>> On 23.07.19 17:19, Jan Kiszka wrote:
>>>> On 23.07.19 16:50, Ralf Ramsauer wrote:
>>>>> Two bad news: Linux's 8250 driver needs patching. At least we need some
>>>>> parameter like 8250.platform=disable to disable the probing for platform
>>>>> uarts. Why?
>>>>>
>>>>> ATM, we must specify 8250.nr_uarts. Otherwise the kernel will touch
>>>>> restricted ports. It does touch those ports, as it lacks ACPI platform
>>>>> information and assumes 'any' platform UART is present.
>>>>
>>>> Yes, nr_uarts is the patch-free approach for now. I once had a hack that
>>>> propagated the information "this is Jailhouse, you may not find platform
>>>> UARTs"
>>>> to the driver. But that was a hack, so I didn't propose that upstream
>>>> along with
>>>> the other x86 changes. Plus, there are cases where we do want to use a
>>>> platform
>>>> uart in the non-root cell.
>>>>
>>>>>
>>>>> I.e.:
>>>>> 8250.nr_uarts=1 only touches 0x3f8
>>>>> 8250.nr_uarts=2 touches 0x3f8 and 0x2f8
>>>>> 8250.nr_uarts=3 touches 0x3f8, 0x2f8, 0x3e9 (?)
>>>>>
>>>>> In addition to that I have a PCI device. And Linux won't probe it until
>>>>> it probed all other PIO ports. If I specify 8250.nr_uarts=1 (as I do
>>>>> want to restrict access to 0x2f8), it will never probe the PCI device.
>>>>>
>>>>> So at the moment, the hack is to set 8250.nr_uarts=4 and permit access
>>>>> to all ports. Yikes. At least I now know that the PCI device basically
>>>>> works, but still, this needs to be patched.
>>>>>
>>>>
>>>> OK, that was probably not yet addressed. We once had a setup with UARTs on
>>>> a PCI
>>>> card, but that machine also had no platform UARTs IIRC.
>>>>
>>>> If there no other way to tell Linux the number of platform UARTs, we will
>>>> have
>>>> to introduce one, for the sake of this use case already.
>>>>
>>>
>>> Maybe we can do something like arch/x86/platform/ce4100/ce4100.c to "tune"
>>> the
>>
>> Thanks for the pointer.
>>
>>> platform UARTs (ce4100_serial_fixup). But it still takes an extension of the
>>> boot protocol to provide Linux with the information about available
>>> platform UARTs.
>>
>> Hm. We do have the comm region... It will hold the config's struct
>> jailhouse_console. We could use this in combination with
>> serial8250_set_isa_configurator.
>>
>> This won't enable all platform uarts, but with this we could
>> automatically enable at least one platform uart + hypervisor debug
>> output. This should be sufficient for most cases.
>
> This is x86 only: If the well-known legacy ports are open in the config and
> also
> the related IRQs, cell-linux could set some to-be-defined flags in the
Hmm. The config (as well as the comm region) lacks the IRQs of the
platform UART. But they should be static for platform UARTs afaict.
> setup_data, and the kernel could tune the platform UART settings accordingly.
> "Should be simple" (TM).
Yep, that wouldn't require any invasive modification of the platform
drivers.
Three flags should be sufficient:
- Use 0x2f8
- Use 0x3f8
- Use dbgcon
Ralf
>
> Jan
>
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