Re: Linux 3.4-rc4

[Jean Delvare <jdelvare@suse.de>]

Hi Luca, Maarten,

On Monday 30 April 2012 01:01:30 pm Luca Tettamanti wrote:
> On Mon, Apr 30, 2012 at 11:07 AM, Maarten Maathuis <madman2003@gmail.com> wrote:
> > On Mon, Apr 30, 2012 at 12:37 AM, Dmitry Torokhov
> >
> > <dmitry.torokhov@gmail.com> wrote:
> >> On Sat, Apr 28, 2012 at 11:33:50AM -0400, Nick Bowler wrote:
> >>> On 2012-04-28 02:19 -0400, Alex Deucher wrote:
> >>> > On Fri, Apr 27, 2012 at 8:39 PM, Nick Bowler <nbowler@elliptictech.com> wrote:
> >>> > > Unfortunately, that's not the end of my VGA-related
> >>> > > regressions. :(
> >>> > >
> >>> > > While tracking down the black screen issue, I've been having
> >>> > > the monitor directly connected to the video card the whole
> >>> > > time, but now when I'm connected through my KVM switch (an
> >>> > > IOGear GCS1804), it appears that something's going wrong with
> >>> > > reading the EDID, because the available modes are all screwed
> >>> > > up (both console and X decide they want to drive the display
> >>> > > at 1024x768).  Here's the output of xrandr on 3.2.15:
> >>> > >
> >>> > >  % xrandr
> >>> > >  Screen 1: minimum 320 x 200, current 1600 x 1200, maximum
> >>> > > 4096 x 4096 VGA-1 connected 1600x1200+0+0 (normal left
> >>> > > inverted right x axis y axis) 352mm x 264mm
> >>> > >     1600x1200      75.0*+   70.0     65.0     60.0
> >>> > >     1280x1024      85.0 +   75.0     60.0
> >>> > >     1920x1440      60.0
> >>> > >     1856x1392      60.0
> >>> > >     1792x1344      60.0
> >>> > >     1920x1200      74.9     59.9
> >>> > >     1680x1050      84.9     74.9     60.0
> >>> > >     1400x1050      85.0     74.9     60.0
> >>> > >     1440x900       84.8     75.0     59.9
> >>> > >     1280x960       85.0     60.0
> >>> > >     1360x768       60.0
> >>> > >     1280x800       84.9     74.9     59.8
> >>> > >     1152x864       75.0
> >>> > >     1280x768       84.8     74.9     59.9
> >>> > >     1024x768       85.0     75.1     75.0     70.1     60.0     43.5     43.5
> >>> > >     832x624        74.6
> >>> > >     800x600        85.1     72.2     75.0     60.3     56.2
> >>> > >     848x480        60.0
> >>> > >     640x480        85.0     75.0     72.8     72.8     66.7     60.0     59.9
> >>> > >     720x400        85.0     87.8     70.1
> >>> > >     640x400        85.1
> >>> > >     640x350        85.1
> >>> > >     320x200       165.1
> >>> > >
> >>> > > And on 3.4-rc4+ (with your patch cherry-picked):
> >>> > >
> >>> > >  % xrandr
> >>> > >  Screen 1: minimum 320 x 200, current 1024 x 768, maximum
> >>> > > 4096 x 4096 VGA-1 connected 1024x768+0+0 (normal left
> >>> > > inverted right x axis y axis) 0mm x 0mm
> >>> > >     1024x768       60.0*
> >>> > >     800x600        60.3     56.2
> >>> > >     848x480        60.0
> >>> > >     640x480        59.9
> >>> > >     320x200       165.1
> >>> > >
> >>> > > Running xrandr on 3.4-rc4+ also causes the screen to go black
> >>> > > for a second when it does not on 3.2.15.  It also causes
> >>> > > several messages of the form
> >>> > >
> >>> > >  [drm] nouveau 0000:01:00.0: Load detected on output B
> >>> > >
> >>> > > to be logged.  Also, looking at
> >>> > > /sys/class/drm/card0-VGA-1/edid I see that it is empty on
> >>> > > 3.4-rc4+ and it is correct on 3.2.15.  Things seem to work OK
> >>> > > when the KVM is not involved.
> >>> >
> >>> > Were you ever able to fetch a EDID with the KVM involved?  KVMs
> >>> > are notorious for not connecting the ddc pins.
> >>>
> >>> Yes, it works on 3.2.15 as described above.
> >>
> >> I have the same (or similar) KVM (not in the office at the moment)
> >> and I can confirm that with newer kernels EDID fecthing in flaky.
> >> It's 50/50 if EDED retrieval succeeds or if it fails with:
> >>
> >> Apr 26 13:06:57 dtor-d630 kernel: [13464.936336]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 26 13:06:57 dtor-d630 kernel: [13464.955317]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 26 13:06:57 dtor-d630 kernel: [13464.973879]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.087659]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.107147]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.126908]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.146277]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.297659]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208 Apr 27 09:13:03 dtor-d630 kernel: [44602.317063]
> >> [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid,
> >> remainder is 208
> >>
> >> Earlier kernels were able to retrieve EDEDs reliably.
> >>
> >> This is with:
> >>
> >> [    1.678392] [drm] nouveau 0000:01:00.0: Detected an NV50
> >> generation card (0x086b00a2)
> >
> > Just a crazy thought, but didn't we change some timings related to
> > EDID retrieval? To make it faster.
> 
> Hum, this commit:
> 
> commit 1849ecb22fb3b5d57b65e7369a3957adf9f26f39
> Author: Jean Delvare <jdelvare@suse.de>
> Date:   Sat Jan 28 11:07:09 2012 +0100
> 
>     drm/kms: Make i2c buses faster
> 
> doubled the data rate but only for radeon and intel drivers. nouveau
> doesn't use the standard i2c-algo-bit helpers (BTW: the
>  cond_resched() has been removed), and AFAICS it's using 1us delay;
>  the other drivers are using 10us, 1us seems a bit too low...

As I read the code, it is actually using a 6 us delay. This is fast
but reasonable, especially when the code handles clock stretching 

Ben Skeggs (Cc'd) rewrote the I2C handling code in the nouveau
driver completely in kernel 3.3:

commit f553b79c03f0dbd52f6f03abe8233a2bef8cbd0d
Author: Ben Skeggs <bskeggs@redhat.com>
Date:   Wed Dec 21 18:09:12 2011 +1000

    drm/nouveau/i2c: handle bit-banging ourselves

    i2c-algo-bit doesn't actually work very well on one card I have access to
    (NVS 300), random single-bit errors occur most of the time - what we're
    doing now is closer to what xf86i2c.c does.

    The original plan was to figure out why i2c-algo-bit fails on the NVS 300,
    and fix it.  However, while investigating I discovered i2c-algo-bit calls
    cond_resched(), which makes it a bad idea for us to be using as we execute
    VBIOS scripts from a tasklet, and there may very well be i2c transfers as
    a result.

    So, since I already wrote this code in userspace to track down the NVS 300
    bug, and it's not really much code - lets use it.

    Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

So if the regression happened between 3.2.15 and 3.4-rc4, that would be
a good candidate.

BTW, Ben, there were two interesting fixes to i2c-algo-bit meanwhile,
you may want to try using it again.

Maarten, another commit you may want to try reverting is
9292f37e1f5c79400254dca46f83313488093825 . If none of the above works,
it would be great if you could test your KVM with another graphics
adapter, so that we know if we are looking for a nouveau-specific bug
or rather an issue in the common i2c or edid code. Otherwise a plain
bisection is probably the way to go.

-- 
Jean Delvare
Suse L3