[U-Boot] [PATCH 06/11] efi_loader: Decouple EFI input/output from stdin/stdout

[Alexander Graf]

On 10/12/2017 04:28 PM, Rob Clark wrote:
> On Thu, Oct 12, 2017 at 9:50 AM, Alexander Graf <agraf at suse.de> wrote:
>> On 10/12/2017 03:40 PM, Rob Clark wrote:
>>> On Thu, Oct 12, 2017 at 9:05 AM, Heinrich Schuchardt <xypron.glpk at gmx.de>
>>> wrote:
>>>>
>>>> On 10/12/2017 02:48 PM, Rob Clark wrote:
>>>>> On Thu, Oct 12, 2017 at 3:15 AM, Alexander Graf <agraf at suse.de> wrote:
>>>>>>
>>>>>>
>>>>>> On 12.10.17 00:07, Rob Clark wrote:
>>>>>>> On Wed, Oct 11, 2017 at 10:45 AM, Alexander Graf <agraf at suse.de>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 10.10.17 14:23, Rob Clark wrote:
>>>>>>>>> In some cases, it is quite useful to have (for example) EFI on
>>>>>>>>> screen
>>>>>>>>> but u-boot on serial port.
>>>>>>>>>
>>>>>>>>> This adds two new optional environment variables, "efiin" and
>>>>>>>>> "efiout",
>>>>>>>>> which can be used to set EFI console input/output independently of
>>>>>>>>> u-boot's input/output.  If unset, EFI console will default to stdin/
>>>>>>>>> stdout as before.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Rob Clark <robdclark at gmail.com>
>>>>>>>>
>>>>>>>> With this patch, we lose the ability to have the efi in/out go to
>>>>>>>> both
>>>>>>>> graphical and serial console, right? This is critical functionality
>>>>>>>> to
>>>>>>>> have, since we don't necessarily know which output/input a user ends
>>>>>>>> up
>>>>>>>> using.
>>>>>>>
>>>>>>> I'll think about how to support iomux.. but some things like console
>>>>>>> size are just not going to work properly there.  And as long as we fix
>>>>>>
>>>>>> Yeah, those probably would need to get special cased.
>>>>>>
>>>>>>> the stdout shenanigans (ie. what I was seeing w/ qemu-x86) you can
>>>>>>> simply not set efiout var and have things working as before, so you
>>>>>>> don't loose any existing functionality (although, like I said, if the
>>>>>>> two different consoles have different sizes things aren't going to
>>>>>>> work properly for anything other than simple cases).
>>>>>>>
>>>>>>> In most cases, the display driver should be able to detect whether a
>>>>>>> display is connected.. this is what I've done on dragonboard410c, so
>>>>>>> if no display plugged in, 'efiout=vidconsole' fails and you fall back
>>>>>>> to serial, else you get efi on screen like you would on a "real"
>>>>>>> computer.  For boards that have a display driver that isn't able to do
>>>>>>> the basic check of whether a cable is plugged in, just don't set
>>>>>>> "efiout" (or fix the display driver) ;-)
>>>>>>
>>>>>> Are you sure that's what happens on a "real" computer? As far as I
>>>>>> remember from all ARM servers running edk2 based firmware that I've
>>>>>> touched so far, the default is always to display on serial *and*
>>>>>> graphical output at the same time.
>>>>>
>>>>> Well, I suppose some of the arm64 server vendors have done a better
>>>>> job than others on firmware.. you'd hope they would probe EDID, and
>>>>> report correct console dimensions based on display resolution, etc.
>>>>>
>>>>> Doing both serial and display works for simple stuff, but it goes
>>>>> badly once the efi payload starts trying to change the cursor position
>>>>> and write to specific parts of the screen (which both Shell.efi and
>>>>> grub try to do).
>>>>>
>>>>> BR,
>>>>> -R
>>>>>
>>>> Hello Rob,
>>>>
>>>> I do not know which program you use for connecting to your serial
>>>> console. I
>>>> use minicom which is a Debian/Ubuntu package. I had no problem using
>>>> grub,
>>>> vim, nano or any other console program.
>>>>
>>>> Minicom just provides a VT100 emulation and that is close enough to what
>>>> Linux expects.
>>> fwiw, I generally use kermit so my terminal emulator is whatever
>>> "xterm" type app I'm using.  (Currently a big fan of Tilix).. but that
>>> isn't so much the issue..
>>>
>>>> So I would not see what should be so special about Shell.efi.
>>> I'm not explaining the problem well, but you can see basically the
>>> same issue if you resize your terminal emulator to something smaller
>>> than what grub/shell/etc think you are using.
>>>
>>> I guess if they just fall back to assuming 80x25 like agraf mentioned,
>>> that would kind of work.  It just means shell or grub will only use
>>> the tiny upper-left corner of your monitor.
>>>
>>>> My U-Boot system all have video but I never have a monitor connected.
>>>>
>>>> So being able to use serial even if video is available is a necessity.
>>> If the video driver doesn't detect that it is unconnected, someone
>>> should really fix that, otherwise you'll have problems booting an
>>> image where grub tries to use gfxterm if GOP is present (but we are
>>> really getting off topic here)
>>>
>>> Either way, you still have the option of not setting efiout (or
>>> setting it to serial)
>>>
>>> But for end users (at least of boards that I care about), if they plug
>>> in a monitor they should get grub on screen.  Not everyone has a
>>> serial cable attached.
>>
>> I fully agree there. The same applies the other way around too. Even if they
>> have a monitor attached, they should get grub on serial if serial is a valid
>> output :). Just attaching a monitor doesn't mean you only use that monitor
>> to control the system.
> We could, I suppose, try probing the serial console's size, as an
> approximation of hotplug detect for serial.  If we timeout without
> getting a response, assume no serial console.
>
> That would also let us pick the minimum of each dimension to report to
> the payload, which is less horrible than just having an 80x25 grub
> menu on your 4k screen.  And if no serial attached, then we can use
> the full screen.

Now we're talking - that sounds much nicer indeed :)


Alex