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    SubjectRe: [PATCH] ACPI / Battery: Return -ENODATA for unknown values in get_property()
    On Thu, Oct 21, 2010 at 09:57:47PM +0200, Rafael J. Wysocki wrote:
    > On Thursday, October 21, 2010, Sitsofe Wheeler wrote:
    > >
    > > It's a shame the previous changes didn't work as they stopped a buggy
    > > upower using the -1 value (and producing a nonsense rate like 8.4e-06)
    >
    > Hmm. So upower _doesn't_ handle -1? What does it do with -1000, then?

    It can't handle that either and outputs a nonsense rate like 0.0084.
    Looking at the code, it would take a very strange value for it to realise
    it is handling a special value as it does arithmetic on the sysfs value
    before doing its check:

    /* get rate; it seems odd as it's either in uVh or uWh */
    energy_rate = fabs (sysfs_get_double (native_path, "current_now") / 1000000.0);

    /* convert charge to energy */
    if (energy == 0) {
    energy = sysfs_get_double (native_path, "charge_now") / 1000000.0;
    if (energy == 0)
    energy = sysfs_get_double (native_path, "charge_avg") / 1000000.0;
    energy *= voltage_design;
    energy_rate *= voltage_design;
    }

    /* some batteries don't update last_full attribute */
    if (energy > energy_full) {
    egg_warning ("energy %f bigger than full %f", energy, energy_full);
    energy_full = energy;
    }

    /* present voltage */
    voltage = sysfs_get_double (native_path, "voltage_now") / 1000000.0;
    if (voltage == 0)
    voltage = sysfs_get_double (native_path, "voltage_avg") / 1000000.0;

    /* ACPI gives out the special 'Ones' value for rate when it's unable
    * to calculate the true rate. We should set the rate zero, and wait
    * for the BIOS to stabilise. */
    if (energy_rate == 0xffff)
    energy_rate = 0;

    By the time the comparison against energy_rate is done the original
    sysfs value has at _least_ divided by 1000000.0 and made positive. Hence
    the test program in my first mail where I mention that 0xfffff produced
    65535.000000, fabs(-1000 / 1000000.0) produced 0.001000 and fabs(-1 /
    1000000.0) produces 0.000001. That's also assuming it doesn't wind up
    multiplying the previous value by voltage_design...

    > > but it's not clear which part of the stack can't handle -ENODATA
    > > perhaps it is another part of the kernel?
    >
    > I don't really think it's a part of the kernel.

    How do I find out which part is not producing those sysfs nodes?

    > > Richard, any chance of upower being changed to test for -1 before doing
    > > doing anything with current_now (
    > > http://cgit.freedesktop.org/DeviceKit/upower/tree/src/linux/up-device-supply.c?id=5387183d53c16a987a0737c1bdec1b62edf3daa6#n561)?
    > > I guess there are a whole bunch of other attributes that could
    > > theoretically be -1 and shouldn't be used if they return it...
    >
    > If user space doesn't handle -1 correctly too, I think the right approach for
    > us should be to use the previous version of the patch and return error code
    > for unknown values.

    So long as sysfs can be made to work properly I am in agreement.

    --
    Sitsofe | http://sucs.org/~sits/


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