From: Andrey Volkov <avolkov@varma-el•com>
To: Sascha Hauer <s.hauer@pengutronix•de>
Cc: Sylvain Munaut <tnt@246tNt•com>,
Paul Mackerras <paulus@samba•org>,
Linuxppc-embedded <Linuxppc-embedded@ozlabs•org>
Subject: Re[2]: MPC5200 + LocalPlus Bus + memcpy
Date: Fri, 7 Apr 2006 12:57:00 +0400 [thread overview]
Message-ID: <646456017.20060407125700@varma-el.com> (raw)
In-Reply-To: <20060407073701.GC10831@localhost.localdomain>
Hello, Sascha.
On Friday, April 7, 2006, Sascha Hauer wrote:
> Hello,
> On Thu, Apr 06, 2006 at 06:21:44PM +0400, Andrey Volkov wrote:
>> Hello, Sascha.
>>
>> On Wednesday, April 5, 2006, Sascha Hauer wrote:
>>
>> > Hi all,
>>
>> > I try to use jffs2 on a flash device connected to the mpc5200
>> > LocalPlus Bus. This bus does not allow misaligned accesses.
>> > The jffs2 code uses memcpy to copy from a word aligned address to an
>> > odd address. The ppc memcpy implementation first copies three bytes to get
>> > the target address word aligned, but then the source address is on an
>> > odd address. The following word accesses on this unaligned address fail
>> > badly.
>> Invalid crc on 'name' field ;)?
> Yes, exactly ;)
:)
>>
>> > I have fixed my problem by modifying the physmap mtd driver, but some
>> > day someone wants to connect SRAM to the LocalPlus Bus and I guess he
>> > will expect memcpy to work.
>> Heh, I'll have same problem. Patch (dirty hack)
>> attached (vs head of vanilla 2.6. tree)
>>
>> > (BTW the arm implementation of memcpy seems to work around this problem)
>> Wrong, memcpy to/from SDRAM _may_ be unaligned, only
>> memcpy_fromio/memcpy_toio _must_ be aligned to even addresses.
> Hm, then a proper fix would be:
> - implement an optimized version of memcpy_fromio/memcpy_toio, this
> could be a version of memcpy which only alignes on the io side
Yes.
> - use memcpy_fromio/memcpy_toio in jffs2 code
They already use it (from jffs2_read/write), only scan.c doesn't
calling this fns.
> Do I see this right?
Yes.
> Is SRAM considered io? I know (Arm-)Boards which do not have SDRAM, they
> run completely from SRAM.
Only LBP demand alignment, SDRAM/DDR and internal SRAM didn't.
--
Regards,
Andrey Volkov
prev parent reply other threads:[~2006-04-07 8:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-05 11:38 MPC5200 + LocalPlus Bus + memcpy Sascha Hauer
2006-04-06 14:21 ` Andrey Volkov
2006-04-07 7:37 ` Sascha Hauer
2006-04-07 8:57 ` Andrey Volkov [this message]
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