linux-kernel - bug in drivers/edac/mpc85xx_edac.c:mpc85xx_mc

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Message-ID: <57AC2FA1761300418C7AB8F3EA493C9702E319DB@HQ-EXCH-5.corp.brocade.com>
Date:	Tue, 28 Apr 2009 18:23:42 -0700
From:	"Jeff Haran" <jharan@...cade.COM>
To:	<linux-kernel@...r.kernel.org>
Subject: bug in drivers/edac/mpc85xx_edac.c:mpc85xx_mc_check()

Hi,

Recent versions of this function contain the following snippets:

    if (err_detect & DDR_EDE_SBE)
        edac_mc_handle_ce(mci, pfn, err_addr & PAGE_MASK,
                  syndrome, row_index, 0, mci->ctl_name);

    if (err_detect & DDR_EDE_MBE)
        edac_mc_handle_ue(mci, pfn, err_addr & PAGE_MASK,
                  row_index, mci->ctl_name);

I am pretty sure the references to PAGE_MASK should be proceeded by a
tilda, as in:

    if (err_detect & DDR_EDE_SBE)
        edac_mc_handle_ce(mci, pfn, err_addr & ~PAGE_MASK,
                  syndrome, row_index, 0, mci->ctl_name);

    if (err_detect & DDR_EDE_MBE)
        edac_mc_handle_ue(mci, pfn, err_addr & ~PAGE_MASK,
                  row_index, mci->ctl_name);

Much as I would like to submit a tested patch like the rest of the
world, I find myself in the situation where the only Freescale target
system I have to test on is running a 3 year old kernel (2.6.14), which
preceeds the introduction of EDAC driver support, at least for
Freescale. So the best I can do is borrow from the new EDAC driver and
backport it to the old kernel.

But I have learned a few things in this process and can thus share what
I've learned as it may be of help to the EDAC driver developers:

1) Before you read the Freescale 8548 CAPTURE_ADDRESS register, you want
to read CAPTURE_ATTRIBUTES first and make sure the VLD bit (least
significant bit in the register) is set or else the data in
CAPTURE_ADDRESS may not be yet valid.

2) When you are done scrubbing the memory with the single bit error, you
want to write 0 to CAPTURE_ATTRIBUTES so as to clear VLD and thus setup
the ECC capture logic to capture the next single bit error.

Please include this email address in responses as I do not subscribe.

Thanks,

Jeff Haran
Brocade
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