linux-kernel - Re: Microblaze early console support

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Date:	Mon, 04 Apr 2011 19:21:58 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Michal Simek <monstr@...str.eu>
CC:	linux-kernel@...r.kernel.org, john.williams@...alogix.com,
	Russell King <linux@....linux.org.uk>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alan Cox <alan@...ux.intel.com>, linux-serial@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: Microblaze early console support

resent.

M

Michal Simek wrote:
> Hi,
> 
> I have one question about early console support on MMU kernel.
> When do you register an early console and what TLB mapping you use?
> 
> For Microblaze I registered it before main memory is setup that's why I was
> hardcoded TLB 63 to 1:1 mapping (virt addr = phys addr). 
> It is output only for early_printk messages but I would like to use it 
> as boot console. There are only some messages that's why TLB 63 was released
> later on.
> That is the current state.
> 
> I have added CON_BOOT flag and register early console by register_console function
> and I allocate TLB 63 for it. But unfortunately I haven't found any function 
> in unregister_console which is called for unregistering to help me to release TLB 63
> when early console is not used. Is there any way how to do it?
> 
> From our experiment in past there is performance degression when kernel can't use
> a TLB that's why I tried to find out a way to release TLB 63.
> This is the reason why I would like to know your opinion if my style is correct 
> or not.
> I created new remap_early_printk function which does ioremap for console space.
> This function is called from setup_arch when memory is setup. Then early mapping of TLB 63
> is automatically released and can be used for Linux purpose.
> Is it correct design how to do it?
> 
> How do you handle it in your arch? Do you register early console before memory initialization
> is done?
> 
> You can also look at my patch I have done.
> 
> Thanks for your suggestions,
> Michal

-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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