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    SubjectRe: applesmc oops in 3.10/3.11
    On Wed, Oct 02, 2013 at 09:47:18AM -0700, Guenter Roeck wrote:
    > On Wed, Oct 02, 2013 at 06:34:18PM +0200, Henrik Rydberg wrote:
    > > > >>One thing I have seen in all logs is the earlier "send_byte fail" message, so
    > > > >>I think that is a pre-requisite.
    > > > >
    > > > >Not necessarily - it could be that the patch actually fixes the root
    > > > >cause. One possible scenario is that on recent SMCs, some of the
    > > > >commands produce more data than we actually read. This would
    > > > >eventually lead to both data corruption and overflow somwhere in the
    > > > >SMC internals. If the original SMC error is interpreted as a read
    > > > >buffer overflow, then that problem should be fixed with this patch.
    > > > >
    > > >
    > > > Good point.
    > > >
    > > > But shouldn't we at least get the "flushed %d bytes" warning message in this case ?
    > >
    > > The explanation I have there is that the (newer) SMC needs the
    > > application to read the 'no more bytes' or it will get confused. It
    > > makes sense, if the number of bytes to read is no longer specified.
    > >
    > You mean that just reading from APPLESMC_CMD_PORT would solve the problem ?
    > That might make sense.

    It also points at the possibility of a smaller patch to test, but I
    have not had the time to check this very deeply myself:

    Thanks,
    Henrik

    From 4451da32414080bd0563ee9e061f19bf90463cc5 Mon Sep 17 00:00:00 2001
    From: Henrik Rydberg <rydberg@euromail.se>
    Date: Wed, 2 Oct 2013 19:15:03 +0200
    Subject: [PATCH] applesmc remedy take 2

    Conjectured problem: there are remnant bytes ready on the data line
    which corrupts the read after a failure.

    Remedy: assuming bit0 is the read valid line, try to flush it before
    starting a new command.

    Tests by Chris suggests reading the status is enough for the problem
    to go away, which is consistent with a change in the SMC interface,
    where the number of bytes to read is no longer specified, but found
    out by reading until end of data.

    Tested on a MacBookAir3,1, but the original problem has not been
    reproduced.
    ---
    drivers/hwmon/applesmc.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
    index 98814d1..c0ff350 100644
    --- a/drivers/hwmon/applesmc.c
    +++ b/drivers/hwmon/applesmc.c
    @@ -230,6 +230,7 @@ static int send_argument(const char *key)

    static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
    {
    + u8 status, data;
    int i;

    if (send_command(cmd) || send_argument(key)) {
    @@ -237,6 +238,7 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
    return -EIO;
    }

    + /* This has no effect on newer (2012) SMCs */
    if (send_byte(len, APPLESMC_DATA_PORT)) {
    pr_warn("%.4s: read len fail\n", key);
    return -EIO;
    @@ -250,6 +252,17 @@ static int read_smc(u8 cmd, const char *key, u8 *buffer, u8 len)
    buffer[i] = inb(APPLESMC_DATA_PORT);
    }

    + /* Read the data port until bit0 is cleared */
    + for (i = 0; i < 16; i++) {
    + udelay(APPLESMC_MIN_WAIT);
    + status = inb(APPLESMC_CMD_PORT);
    + if (!(status & 0x01))
    + break;
    + data = inb(APPLESMC_DATA_PORT);
    + }
    + if (i)
    + pr_warn("flushed %d bytes, last value is: %d\n", i, data);
    +
    return 0;
    }

    --
    1.8.3.4


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