linux-kernel - Re: [PATCH] ARM: mmp: map sram as MT_MEMORY rather than MT

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Date:	Tue, 23 Aug 2011 16:22:17 +0800
From:	Haojian Zhuang <haojian.zhuang@...vell.com>
To:	Leo Yan <leoy@...vell.com>
CC:	Andres Salomon <dilinger@...ued.net>,
	Eric Miao <eric.y.miao@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Haojian Zhuang <hzhuang1@...vell.com>,
	Jon Nettleton <jon.nettleton@...il.com>
Subject: Re: [PATCH] ARM: mmp: map sram as MT_MEMORY rather than MT_DEVICE

On Tue, 2011-08-23 at 00:48 -0700, Leo Yan wrote:
> 
> On 08/23/2011 10:08 AM, Andres Salomon wrote:
> > On Tue, 23 Aug 2011 08:07:41 +0800
> > Eric Miao<eric.y.miao@...il.com>  wrote:
> >
> >> On Tue, Aug 23, 2011 at 7:47 AM, Andres Salomon<dilinger@...ued.net>
> >> wrote:
> >>> The sram code allocates memory with ioremap, which assumes MT_DEVICE
> >>> for memory protections.  This explodes when we map sram for power
> >>> management purposes and then attempt to execute it (jump_to_lp_sram)
> >>> on the OLPC XO-1.75.  Instead, we want to specify MT_MEMORY, which
> >>> doesn't set the L_PTE_XN bit.
> >>>
> >>> Signed-off-by: Andres Salomon<dilinger@...ued.net>
> >>> ---
> >>>   arch/arm/mach-mmp/sram.c |    4 +++-
> >>>   1 files changed, 3 insertions(+), 1 deletions(-)
> >>>
> >>> Eric, this patch is against the devel branch of your pxa tree.
> >>>
> >>> diff --git a/arch/arm/mach-mmp/sram.c b/arch/arm/mach-mmp/sram.c
> >>> index 4304f95..ca4d3c1 100644
> >>> --- a/arch/arm/mach-mmp/sram.c
> >>> +++ b/arch/arm/mach-mmp/sram.c
> >>> @@ -21,6 +21,7 @@
> >>>   #include<linux/err.h>
> >>>   #include<linux/slab.h>
> >>>   #include<linux/genalloc.h>
> >>> +#include<asm/mach/map.h>
> >>>
> >>>   #include<mach/sram.h>
> >>>
> >>> @@ -87,7 +88,8 @@ static int __devinit sram_probe(struct
> >>> platform_device *pdev)
> >>>
> >>>         info->sram_phys   = (phys_addr_t)res->start;
> >>>         info->sram_size   = resource_size(res);
> >>> -       info->sram_virt   = ioremap(info->sram_phys,
> >>> info->sram_size);
> >>> +       info->sram_virt   = __arm_ioremap(info->sram_phys,
> >>> info->sram_size,
> >>> +                                         MT_MEMORY);
> >>
> >> I doubt MT_MEMORY is intended for use with __arm_ioremap(). There
> >> could be other way around to the L_PTE_XN bit.
> >>
> >> One other way I'm actually thinking of is to add the SRAM mapping to
> >> mmp_map_io(). The difference of SRAM offset/size may result the
> >> separation of mmp_map_io() into {pxa168,pxa910,mmp2}_map_io()
> >> if necessary.
> >>
> >
> > I guess I don't follow.  I think you're talking about adding it to the
> > standard_io_desc array, but that would require having it pre-mapped and
> > knowing the virtual address.  Or were you planning to ioremap it?
> 
> I missed the L_PTE_XN bit.
> The patch is originally for audio sram, so use the ioremap is ok for 
> that. But for the internal sram we should need the different mapping 
> property.
> 
> so far, the standard_io_desc is shared by pxa168/pxa910/mmp2;
> we can not add the sram's entry into it for now sram is only dedicated
> to mmp2; just like Eric's suggestion, we need mmp2_map_io() only for
> mmp2, and add the sram's entries into the structure.
> if so, we need transfer the mapped info into the sram module,
> and sram module just keep the info and do not need remap it again.
> 
> so what's your opinion?

Could we use resource or platform data to specify sram is used for
device or memory? If so, it may be helpful to customize.

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