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    SubjectRe: Linux 3.4-rc4
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    On Wed, 2012-05-02 at 09:54 +0200, Jean Delvare wrote:
    > 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.
    Hey Jean,

    Thanks! I did notice this, and your email, a while back. I just
    haven't yet had the time to see how the NVS300 goes now. I do
    definitely plan on taking a peek however.

    Ben.

    >
    > 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.
    >




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