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Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs.

From Greg KH <gregkh@linuxfoundation.org>
Newsgroups linux.kernel
Subject Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs.
Date 2016-04-29 19:40 +0200
Message-ID <rtkyu-1rQ-5@gated-at.bofh.it> (permalink)
References (3 earlier) <rtbOx-2Gn-7@gated-at.bofh.it> <rtimZ-8fU-5@gated-at.bofh.it> <rtiGl-8rB-13@gated-at.bofh.it> <rtiZI-a2-7@gated-at.bofh.it> <rtj9o-xI-11@gated-at.bofh.it>
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On Fri, Apr 29, 2016 at 05:02:57PM +0100, Richard W.M. Jones wrote:
> On Fri, Apr 29, 2016 at 08:54:13AM -0700, Greg KH wrote:
> > You are trying to take a generalized kernel and somehow "know" about the
> > hardware ahead of time it is going to run on.  That seems like two
> > conflicting requirements, don't you agree?
> 
> We would have the 8250 serial port in any kernel.  Even if Fedora
> kernel maintainers allowed us to have specialized kernels for each
> purpose, I would use the simple ISA serial port here because it allows
> us to capture debug messages very early in the boot.  Alternatives
> like virtio-console don't allow that.
> 
> The kernel does know what hardware it's running on - via the CPUID
> hypervisor leaf.  It's also possible for us to tell the kernel about
> the hardware using the command line, ACPI[*], DT, etc.  I'd really
> like to tell the kernel this is a 16550A, not broken, you don't need
> to spend time testing that.

Then properly describe the device to the kernel in a way that you know
you don't have to do the 20ms sleep from your system configuration file
(acpi, dt, etc.)

good luck,

greg k-h

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Thread

[PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 00:20 +0200
  Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 01:00 +0200
    Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 10:20 +0200
      Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 17:20 +0200
        Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 17:40 +0200
          Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 18:00 +0200
            Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. "Richard W.M. Jones" <rjones@redhat.com> - 2016-04-29 18:10 +0200
              Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Greg KH <gregkh@linuxfoundation.org> - 2016-04-29 19:40 +0200
          Re: [PATCH] 8250: Hypervisors always export working 16550A UARTs. Don Dutile <ddutile@redhat.com> - 2016-04-29 20:20 +0200

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