[linux-sunxi] Re: [PATCH 4/4] simplefb: add clock handling code

[jonsmirl at gmail.com]

On Thu, Aug 28, 2014 at 12:25 PM, Michal Suchanek <hramrach at gmail.com> wrote:
> On 28 August 2014 16:33, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
>> On Thu, Aug 28, 2014 at 10:20 AM, Geert Uytterhoeven
>> <geert at linux-m68k.org> wrote:
>>> On Thu, Aug 28, 2014 at 3:22 PM, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
>>>>> 2) We don't want to hardcode these clocks into the kernel (sunxi) clk
>>>>> driver, instead the bootloader should tell the kernel about these clocks.
>>>>>
>>>>> So the only point of discussion left seems to be how to do 2...
>>>>
>>>> Wouldn't it be a lot simpler just to use existing fbdev (not KMS) and
>>>> whip together a device specific driver that claims the proper
>>>> resources? And just implement the minimal about of fbdev possible?
>>>> fbdev already is a driver library.
>>>
>>> Like... drivers/video/fbdev/offb.c?
>>
>> I'd probably reclassify drivers/video/fbdev/simplefb.c as a skeleton
>> and use it as a template for making device specific versions of it.
>>
>> I don't see why there is so much resistance to just making device
>> specific fb drivers.  Whenever the KMS driver gets written just
>> disable the device specific fb driver in the build.
>
> Except that is not the goal here. The simplefb or whatever replacement
> is supposed to stay as a  generic driver compiled into kernel whereas

There is no generic solution to this problem as this entire thread has
illustrated. The clocks/regulators needed by each SOC vary.

So there are two solutions..
1) modify simplefb to have some kind of heuristic that tries to guess
what needs to be protected. A heuristic that is probably going to fail
on every new SOC.

2) Spend a day implementing a device specific fbdev driver that does
the correct thing all of the time. These drivers would sit in initrd
and load before the clock/regulator clean up shuts everything off. Use
the existing simplefb code as a template for doing this.


> the complete platform-specific driver is supposed to be provided as
> module and loaded at the init system's leasure sometime during boot.
> This way you can have generic distribution kernel which supports many
> devices but does not have built-in support for every graphics
> hardware.
>
> Thanks
>
> Michal
>
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-- 
Jon Smirl
jonsmirl at gmail.com