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    Subject[PATCH 4.9 04/77] rtc-opal: Fix handling of firmware error codes, prevent busy loops
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Stewart Smith <stewart@linux.vnet.ibm.com>

    commit 5b8b58063029f02da573120ef4dc9079822e3cda upstream.

    According to the OPAL docs:
    skiboot-5.2.5/doc/opal-api/opal-rtc-read-3.txt
    skiboot-5.2.5/doc/opal-api/opal-rtc-write-4.txt

    OPAL_HARDWARE may be returned from OPAL_RTC_READ or OPAL_RTC_WRITE and
    this indicates either a transient or permanent error.

    Prior to this patch, Linux was not dealing with OPAL_HARDWARE being a
    permanent error particularly well, in that you could end up in a busy
    loop.

    This was not too hard to trigger on an AMI BMC based OpenPOWER machine
    doing a continuous "ipmitool mc reset cold" to the BMC, the result of
    that being that we'd get stuck in an infinite loop in
    opal_get_rtc_time().

    We now retry a few times before returning the error higher up the
    stack.

    Fixes: 16b1d26e77b1 ("rtc/tpo: Driver to support rtc and wakeup on PowerNV platform")
    Cc: stable@vger.kernel.org # v3.19+
    Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/rtc/rtc-opal.c | 12 ++++++++++--
    1 file changed, 10 insertions(+), 2 deletions(-)

    --- a/drivers/rtc/rtc-opal.c
    +++ b/drivers/rtc/rtc-opal.c
    @@ -58,6 +58,7 @@ static void tm_to_opal(struct rtc_time *
    static int opal_get_rtc_time(struct device *dev, struct rtc_time *tm)
    {
    long rc = OPAL_BUSY;
    + int retries = 10;
    u32 y_m_d;
    u64 h_m_s_ms;
    __be32 __y_m_d;
    @@ -67,8 +68,11 @@ static int opal_get_rtc_time(struct devi
    rc = opal_rtc_read(&__y_m_d, &__h_m_s_ms);
    if (rc == OPAL_BUSY_EVENT)
    opal_poll_events(NULL);
    - else
    + else if (retries-- && (rc == OPAL_HARDWARE
    + || rc == OPAL_INTERNAL_ERROR))
    msleep(10);
    + else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
    + break;
    }

    if (rc != OPAL_SUCCESS)
    @@ -84,6 +88,7 @@ static int opal_get_rtc_time(struct devi
    static int opal_set_rtc_time(struct device *dev, struct rtc_time *tm)
    {
    long rc = OPAL_BUSY;
    + int retries = 10;
    u32 y_m_d = 0;
    u64 h_m_s_ms = 0;

    @@ -92,8 +97,11 @@ static int opal_set_rtc_time(struct devi
    rc = opal_rtc_write(y_m_d, h_m_s_ms);
    if (rc == OPAL_BUSY_EVENT)
    opal_poll_events(NULL);
    - else
    + else if (retries-- && (rc == OPAL_HARDWARE
    + || rc == OPAL_INTERNAL_ERROR))
    msleep(10);
    + else if (rc != OPAL_BUSY && rc != OPAL_BUSY_EVENT)
    + break;
    }

    return rc == OPAL_SUCCESS ? 0 : -EIO;

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