linux-kernel - Re: [PATCH] 8250: option 'force

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Date:	Thu, 28 Jul 2016 07:47:04 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Max Staudt <mstaudt@...e.de>
Cc:	Theodore Ts'o <tytso@....edu>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 8250: option 'force_polling' for buggy IRQs

On Thu, Jul 28, 2016 at 11:59:20AM +0200, Max Staudt wrote:
> On 07/27/2016 03:33 PM, Theodore Ts'o wrote:
> > On Wed, Jul 27, 2016 at 02:14:24PM +0200, Max Staudt wrote:
> >>> If you set the IRQ to 0 it should poll anyway (0 means 'no IRQ') so I
> >>> don't think the option is needed. At least it seems sufficient to get me
> >>> by when I meet buggy PC BIOSes and the like
> >>
> >> That's exactly what the patch does - but if there is already a way to set the
> >> IRQ to 0, I would of course prefer to use that.
> >>
> >> It seems I haven't found the trick you're using - could you please tell me how
> >> you set the IRQ to 0?  I can't change it in the BIOS, so I have to do it at
> >> the kernel level at the latest.
> > 
> > So the problem is that you can't use setserial because you want to use
> > this port for your console?  And so you don't want to set it in an initscript?
> 
> Exactly. There is no initscript when I use rdinit=/bin/bash, so I have no choice
> but to set it in the kernel. As soon as /bin/bash accesses /dev/ttyS0, the
> console hangs.
> 
> 
> > The one thing which is really unfortunate with this patch is that it's
> > a global, so it forces polling for *all* serial ports.  And it may be
> > that it's only base ports on the motherboard which needs this hack.
> 
> I agree, and I thought about it, but since this is meant for a very limited
> audience, I think a catch-all is the easiest solution - both in terms of
> implementation as well as ease of use.
> 
> It's not meant for general consumption anyway.

Then I really don't want to have to maintain and support such a kernel
option for 20+ years, just because of one broken system out there like
this.  There are workarounds for this, as you have seen, including
booting with a "real" userspace, so I don't want to take this patch.

thanks,

greg k-h