linux-kernel - Re: [PATCH] ignore ,keep for efi earlyprintk

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Date:	Tue, 29 Apr 2014 18:03:52 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	matt.fleming@...el.com, hpa@...or.com, akpm@...ux-foundation.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH] ignore ,keep for efi earlyprintk

On 04/29/14 at 10:45am, Matt Fleming wrote:
> On Sat, 26 Apr, at 03:28:21PM, Dave Young wrote:
> > 
> > There's other kernel messages without appending ,keep.
> > 
> > Also console=ttyS0 does not work with earlyprintk=efi,keep, removing
> > ,keep it works well.
> 
> Try console=efi

With console=efi, it also hangs the screen is not readable. When I add both console=efi
and console=ttyS0, in serial console output looks like it hangs while mounting rootfs. 
On screen it's same as console=efi only case.

I justed tested on qemu.

> 
> > > > Actually efi earlyprintk is using __init functions such as early_ioremap etc.
> > > > Thus efi earlyconsole can not be kept.
> > >  
> > > Urgh, good point, that's a bug. However I'm sure I've had this working
> > > in the past and have in fact used it to debug stuff.
> > > 
> > > Could you try and fix this up so it works with 'keep'?
> > 
> > Will do. I want use ioremap when it is available but it's hard to decide
> > where to add the code.
> > 
> > I'm thinking to do below:
> > 1. ioremap the whole framebuffer like: efi_fb = ioremap(lfb_base, lfb_size) in the
> >    function efi_enter_virtual_mode because ioremap should be usable then.
> > 
> > 2. add two functions for earlyprintk use (scrollup, write, etc.) 
> > __init_refok void * get_vaddr(unsigned long start, unsigned long len)
> > {
> > 	unsigned long base;
> > 
> > 	base = boot_params.screen_info.lfb_base;
> > 	if (efi_fb)
> > 		return (efi_fb + start - base);
> > 	else
> > 		return early_ioremap(start, len);
> > }
> > 
> > __init_refok void put_vaddr(void *addr, unsigned long len)
> > {
> > 	if (!efi_fb)
> > 		early_iounmap(addr, len);
> > }
> > 
> > But it does not sound good to add the ioremap in enter virtual mode funtion.   
> > 
> > Please help if you have any other better idea.
> 
> I would just replace the existing calls to early_ioremap() with
> efi_ioremap() and implement it like so (all in
> arch/x86/platform/efi/early_printk.c),
> 
> static void *efi_ioremap(resource_size_t phys_addr, unsigned long size)
> {
> 	if (system_state == SYSTEM_BOOTING)
> 		return early_ioremap(phys_addr, size);
> 
> 	return ioremap(phys_addr, size);
> }
> 
> At least I think SYSTEM_BOOTING is the correct way to figure out when to
> use early_ioremap(), I'm open to other suggestions though.

I also thought about this before, but I remember it hangs before system state
changing.

The flow is like below, I added some debug printk, only the ones before free_initmem()
shows in log. Thus I guess this will not work. But I can have a try. 
        kernel_init_freeable();
        /* need to finish all async __init code before freeing the memory */
        async_synchronize_full();
        free_initmem();
        mark_rodata_ro();
        system_state = SYSTEM_RUNNING; 

Thanks
Dave
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