Re: [PATCH] fb: Rework locking to fix lock ordering on takeover

From: Alexander Holler
Date: Fri Jan 04 2013 - 08:36:27 EST

Am 04.01.2013 14:25, schrieb Alan Cox:
On Fri, 04 Jan 2013 13:50:37 +0100
Alexander Holler <holler@xxxxxxxxxxxxx> wrote:

Am 28.12.2012 13:40, schrieb Borislav Petkov:
On Fri, Dec 28, 2012 at 07:50:27PM +0800, Shawn Guo wrote:

Cool, works fine here too. Is Linus on CC? (/me checks.. ) Yes he is,

Linus, Alan's patch works at least in 2 cases, you might consider
picking it up directly since the fb maintainer is absent, reportedly.

Btw. I think all the usb-fb's (udlfb, smscufx and udl) are broken, at
least on ARM(v5). When I have linked in udlfb the following happens on
boot (with an attached USB-LCD and with or without the "Rework locking

They are broken if used as the system console (has been known for years).

Ah. Thats why I didn't see it before. Usually I've used the serial as system console. So thats why it worked before. ;)

Perhaps your x86 test has the system console still on another device ?

Exactly thats the case. Thanks for pointing it out.

For the udl layer it shouldn't matter as Dave Airlie wrote a DRM driver
for udl which obsoletes the old fb layer one and works much better
(although the error handling is still totally broken and leaks like a
sieve if it fails)

Fixing the console isn't that difficult - you just need to make your
device queue the console I/O to a worker thread of some kind. We don't

That is what I wanted to try next. ;)

want to do that by default because we want to get the messages out
reliably and immediately on saner hardware. Given there are several
such cases a general helper and a console "I am crap" flag might be better
than hacking each driver.

All those drivers look very similiar. I will see if I'm successfull in writing such an IamCrapHelper. Might need some time, but I will post a patch for review, if I've done and tested it. I'm only using the USB-LCD on occasion, so it doesn't have high priority for me because I don't really need it.

Thanks for the hints.


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