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crocket
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Joined: 29 Apr 2017
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PostPosted: Sat Mar 02, 2019 11:36 pm    Post subject: The horror story of linux kernel Reply with quote

Let me explain the horror story. (The short version // Linux kernel let dependencies slip through cracks. It took days for a mere user like me to debug the issue.)

DRM_RADEON should depend on DRM_FBDEV_EMULATION and I2C_CHARDEV, but it doesn't.
Without DRM_FBDEV_EMULATION, DRM_RADEON loses video signal on all virtual consoles and garbles an X session for the first few seconds.
Without I2C_CHARDEV, DRM_RADEON becomes white on all virtual consoles.

DRM_RADEON should not initialize before I2C_CHARDEV. Because DRM_RADEON is oblivious of I2C_CHARDEV, DRM_RADEON may or may not initialize before I2C_CHARDEV.
If I2C_CHARDEV=y and DRM_RADEON=m, DRM_RADEON never initializes before I2C_CHARDEV does. If I2C_CHARDEV=y and DRM_RADEON=y, DRM_RADEON may or may not initialize before I2C_CHARDEV does.

It took days of trial and error to pinpoint the cause of DRM_RADEON's issue. At first, I just guessed relevant kernel config options, but it was too inefficient. Eventually, I started comparing differences between kernel configs that work and those that don't.
Based on differences, my trials became more accurate. Eventually, I narrowed the issue down to DRM_FBDEV_EMULATION and I2C_CHARDEV.

What a horror story. I assumed linux kernel wouldn't let dependencies slip through cracks.


Last edited by crocket on Sun Mar 03, 2019 1:12 am; edited 1 time in total
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NeddySeagoon
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PostPosted: Sun Mar 03, 2019 12:17 am    Post subject: Reply with quote

crocket,

Quote:
I assumed ...

Rule 1. Assume nothing.

I spent most of a day on IRC helping fix sound. Lots of kernel rebuilds later, it was established that the kernel was correct a long time age. It just wasn't being installed.
I assumed ...
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bammbamm808
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PostPosted: Sun Mar 03, 2019 8:26 pm    Post subject: Re: The horror story of linux kernel Reply with quote

crocket wrote:
It took days of trial and error


Welcome to the world of FOSS.
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freke
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PostPosted: Sun Mar 03, 2019 8:54 pm    Post subject: Reply with quote

NeddySeagoon wrote:
crocket,

Quote:
I assumed ...

Rule 1. Assume nothing.

I spent most of a day on IRC helping fix sound. Lots of kernel rebuilds later, it was established that the kernel was correct a long time age. It just wasn't being installed.
I assumed ...


The quote really is: https://www.youtube.com/watch?v=7rr88Szc5q0
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proteusx
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PostPosted: Mon Mar 04, 2019 1:19 am    Post subject: Reply with quote

So, for now, what are the best settings for I2C_CHARDEV, DRM_FBDEV_EMULATION and DRM_RADEON?
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crocket
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PostPosted: Mon Mar 04, 2019 3:12 am    Post subject: Reply with quote

proteusx wrote:
So, for now, what are the best settings for I2C_CHARDEV, DRM_FBDEV_EMULATION and DRM_RADEON?


I2C_CHARDEV=y
DRM_FBDEV_EMULATION=y
DRM_RADEON=m
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