[Intel-gfx] Contribute to DRM

[Intel-gfx] Contribute to DRM

[Lucas Tanure]

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Hi,

I would like to start to contribute to drm part of kernel. I tried a few
things:

- Compiled linux-next tree using C=1 (sparse) to find things to improve.
But couldn't find any problem or issue.
- I looked in "www.x.org/wiki/DRMJanitors/" for stuff to do, but seems that
most of them are already done when I checked the code.

- Compiled and run the linux-next tree to test the code. And for this I got
the warning below.
I tried to compile a few older versions of linux-next in order to find the
offending commit. But I didn't succeed, many commits don't boot at all, and
is difficult to get more information about the status of the warning for
that version.

So, I would like some tips about how to debug DRM code, how to test, how to
get more information about issues.
What I do is :
- Compile and run
- Restart to a good kernel
- "journalctl --boot=-1"  to see if I got any warning on previous kernel

Also, if any developer needs/wants some help and it's ok to guide a new guy
in DRM code, I would like to get help about tasks to do, things to
clean/improve.
I'm reading https://www.kernel.org/doc/htmldocs/drm/ to start, and I have
done a few courses from linux foundation.

Thanks
Best Regards

--
Lucas Tanure
br.linkedin.com/in/lucastanure

WARNING: CPU: 3 PID: 243 at drivers/gpu/drm/drm_drv.c:569
drm_dev_alloc+0x251/0x320 [drm]()
Modules linked in: i915(+) joydev input_leds mousedev intel_rapl iosf_mbi
x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm ttm
hid_generic drm_kms_helper crct10dif_pclmul snd_hda_intel crc32_pclmul
usbhid snd_hda_codec crc32c_intel drm hid ghash_clmulni_intel snd_hda_core
eeepc_wmi asus_wmi aesni_intel iTCO_wdt sparse_keymap snd_hwdep led_class
aes_x86_64 lrw snd_pcm iTCO_vendor_support rfkill mxm_wmi evdev gf128mul
intel_gtt e1000e glue_helper mac_hid snd_timer syscopyarea ablk_helper
cryptd sysfillrect psmouse snd sysimgblt pcspkr fb_sys_fops ptp mei_me
i2c_i801 i2c_algo_bit soundcore mei shpchp i2c_core pps_core lpc_ich
serio_raw wmi fan battery processor thermal video button sch_fq_codel
ip_tables x_tables ext4 crc16 mbcache jbd2 sd_mod atkbd libps2 ahci libahci
libata
 xhci_pci xhci_hcd ehci_pci ehci_hcd scsi_mod usbcore usb_common i8042 serio
CPU: 3 PID: 243 Comm: systemd-udevd Not tainted 4.2.0-next-20150912-ARCH #5
Hardware name: System manufacturer System Product Name/Maximus IV GENE-Z,
BIOS 3603 11/09/2012
 0000000000000000 000000005ca47666 ffff88060f70b9d0 ffffffff812b9159
 0000000000000000 ffff88060f70ba08 ffffffff81074e62 ffff880612d39000
 ffffffffa06c7100 ffff880612f66098 ffffffffa06c7100 ffffffffa0691760
Call Trace:
 [<ffffffff812b9159>] dump_stack+0x4b/0x72
 [<ffffffff81074e62>] warn_slowpath_common+0x82/0xc0
 [<ffffffff81074faa>] warn_slowpath_null+0x1a/0x20
 [<ffffffffa0422291>] drm_dev_alloc+0x251/0x320 [drm]
 [<ffffffffa0424d0b>] drm_get_pci_dev+0x3b/0x1e0 [drm]
 [<ffffffffa05dd2d4>] i915_pci_probe+0x34/0x50 [i915]
 [<ffffffff812fdec5>] local_pci_probe+0x45/0xa0
 [<ffffffff812fde10>] ? pci_match_device+0xe0/0x110
 [<ffffffff812ff053>] pci_device_probe+0x103/0x150
 [<ffffffff813d7942>] driver_probe_device+0x222/0x490
 [<ffffffff813d7c34>] __driver_attach+0x84/0x90
 [<ffffffff813d7bb0>] ? driver_probe_device+0x490/0x490
 [<ffffffff813d557c>] bus_for_each_dev+0x6c/0xc0
 [<ffffffff813d70fe>] driver_attach+0x1e/0x20
 [<ffffffff813d6c4b>] bus_add_driver+0x1eb/0x280
 [<ffffffff813d8540>] driver_register+0x60/0xe0
 [<ffffffff812fd73c>] __pci_register_driver+0x4c/0x50
 [<ffffffffa0424f90>] drm_pci_init+0xe0/0x110 [drm]
 [<ffffffffa06e6000>] ? 0xffffffffa06e6000
 [<ffffffffa06e60a4>] i915_init+0xa4/0xab [i915]
 [<ffffffff81002123>] do_one_initcall+0xb3/0x200
 [<ffffffff81199801>] ? __vunmap+0x91/0xe0
 [<ffffffff811589a0>] do_init_module+0x5f/0x1ef
 [<ffffffff810fa707>] load_module+0x2197/0x27e0
 [<ffffffff810f7550>] ? symbol_put_addr+0x50/0x50
 [<ffffffff81188695>] ? __pte_alloc_kernel+0xa5/0xf0
 [<ffffffff810fae9e>] SyS_init_module+0x14e/0x190
 [<ffffffff8157046e>] entry_SYSCALL_64_fastpath+0x12/0x71
---[ end trace d2652104b24a32ff ]---

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Re: Contribute to DRM

[Jani Nikula]

On Tue, 15 Sep 2015, Lucas Tanure <tanure@linux.com> wrote:
> Hi,
>
> I would like to start to contribute to drm part of kernel. I tried a few
> things:
>
> - Compiled linux-next tree using C=1 (sparse) to find things to improve.
> But couldn't find any problem or issue.
> - I looked in "www.x.org/wiki/DRMJanitors/" for stuff to do, but seems that
> most of them are already done when I checked the code.
>
> - Compiled and run the linux-next tree to test the code. And for this I got
> the warning below.
> I tried to compile a few older versions of linux-next in order to find the
> offending commit. But I didn't succeed, many commits don't boot at all, and
> is difficult to get more information about the status of the warning for
> that version.

I think especially for getting started linux-next is too volatile. I'd
go for Linus' git master first. After that, I'd still recommend driver
specific trees rather than linux-next.

drm/i915 branches are at http://cgit.freedesktop.org/drm-intel

> So, I would like some tips about how to debug DRM code, how to test, how to
> get more information about issues.
> What I do is :
> - Compile and run
> - Restart to a good kernel
> - "journalctl --boot=-1"  to see if I got any warning on previous kernel
>
> Also, if any developer needs/wants some help and it's ok to guide a new guy
> in DRM code, I would like to get help about tasks to do, things to
> clean/improve.
> I'm reading https://www.kernel.org/doc/htmldocs/drm/ to start, and I have
> done a few courses from linux foundation.

It's pretty hard to give generic advise; what works for me doesn't
necessarily work for you. With that out of the way, try focusing on some
detail and figure out how it works. Or find an itch and scratch it,
maybe a bug you experience. Or a bug someone else has and you can
reproduce it (product "DRI" at https://bugs.freedesktop.org/, you'll
probably need to narrow the search down). Expand on related details,
etc.

Based on the warn you seem to have an Intel GPU, so you might find
https://01.org/linuxgraphics/documentation helful.

You might also get faster replies on IRC at #dri-devel and #intel-gfx on
freenode, as long as you don't bug people too much. ;)

HTH,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center
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