On Wed, Oct 22, 2014 at 06:35:53PM +0200, Pali Rohár wrote: > On Wednesday 22 October 2014 18:19:47 Guenter Roeck wrote: > > On Wed, Oct 22, 2014 at 02:29:06PM +0200, Pali Rohár wrote: > > > On Tuesday 21 October 2014 06:27:23 Guenter Roeck wrote: > > > > On 10/20/2014 09:46 AM, Pali Rohár wrote: > > > > > Ok, I will describe my problem. Guenter, maybe you can > > > > > find another solution/fix for it. > > > > > > > > > > Calling i8k_get_temp(3) on my laptop without > > > > > I8K_TEMPERATURE_BUG always returns value 193 (which is > > > > > above I8K_MAX_TEMP). > > > > > > > > > > When I8K_TEMPERATURE_BUG is enabled (by default) then > > > > > i8k_get_temp(3) returns value from prev[3] and store new > > > > > value I8K_TEMPERATURE_BUG to prev[3]. Value in prev[3] > > > > > is initialized to 0. > > > > > > > > > > What I want to achieve is: when i8k_get_temp() for > > > > > particular sensor id always returns invalid value (> > > > > > I8K_MAX_TEMP) then we should totally ignore sensor with > > > > > that id and do not export it via hwmon. > > > > > > > > > > My solution is: initialize prev[id] to I8K_MAX_TEMP, so > > > > > on invalid data first call to i8k_get_temp(id) returns > > > > > I8K_MAX_TEMP. Then in i8k_init_hwmon check if value is > > > > > < I8K_MAX_TEMP and if not ignore sensor id. > > > > > > > > > > Guenter, it is clear now? Are you ok that we should > > > > > ignore sensor if always report value above > > > > > I8K_MAX_TEMP? If you do not like my solution/patch for > > > > > it, can you specify how other can it be fixed? > > > > > > > > I still don't see the point in initializing prev[]. > > > > > > Now prev[] is initialized to 0. It means that first call > > > i8k_get_temp() (with sensor id which return value > > > > I8K_MAX_TEMP) returns 0. Second and other calls returns > > > I8K_MAX_TEMP. > > > > > > So point is to return same value for first and other calls. > > > > Yes, I realized that after I sent my previous mail. > > > > > > Yes, I am ok with ignoring sensor values if the reported > > > > temperature is above I8K_MAX_TEMP. I am just not sure if > > > > we should check against I8K_MAX_TEMP or against, say, > > > > 192. Reason is that we do know that the sensor can > > > > erroneously return 0x99 on some systems once in a while. > > > > We would not want to ignore those sensors just because > > > > they happen to report 0x99 during initialization. > > > > > > > > So maybe make it > > > > > > > > if (err >= 0 && err < 192) > > > > > > > > and add a note before the first if(), explaining that > > > > higher values suggest that there is no sensor attached. > > > > > > > > Thanks, > > > > Guenter > > > > > > Right, now we need to decide which magic constant to use... > > > > > > And now I found another problem :-) > > > > > > On my laptop i8k_get_temp(3) not always return value 193. It > > > is only when AMD graphics card is turned off. When card is > > > on i8k_get_temp(3) returns same value as temperature hwmon > > > part from radeon DRM driver. > > > > Can you turn the GPU on or off during runtime ? > > That would make it really tricky to handle the situation. > > > > Yes. New laptops with Nvidia Optimus or AMD PowerXpress or Enduro > technology are designed to automatically turn off secondary GPU > when is not in use. And nouveau/radeon drivers together with > vga_switcheroo implements this dynamic power on/off. > > > > So it looks like that on my laptop i8k sensor with id 3 > > > reports GPU temperature. > > > > > > When card is turned off radeon driver reports -EINVAL for > > > temperature hwmon sysnode. > > > > > > So now I think i8k could not ignore sensor totally as it can > > > be mapped to some HW which can be dynamically turned on/off > > > (like my graphics card). > > > > > > So what do you think about reporting -EINVAL instead > > > I8K_MAX_TEMP when dell SMM returns value above > > > I8K_MAX_TEMP? > > > > -EINVAL is supposed to mean "Invalid Argument", so it really > > has ia different semantics. We could use -ENXIO, "No such > > device or address", which seems more appropriate. > > > > I prefer to use -EINVAL because other driver (radeon) is using it > and userspace "sensors" programs handle EINVAL and show "N/A" in > output instead reporting some error about reading value. If > nothing else consistency (with other drivers) is my argument. > Ok, if sensors implements it that way then let's do it.
> > Overall, I think the entire error handling is broken and > > should be replaced. One option would be to explicitly check > > for 0x99 and, if detected, go to sleep for, say, 100ms and > > try again. If it still fails, and for all other bad values, > > return -ENXIO. Then the calling code can either return the > > error to user space in the show function, or not install the > > sensor in the probe function. > > > > Does that make sense ? > > > > Yes, replacing error handling with retry call (after some sleep) > is better then current code (which returns previous value or > returns I8K_MAX_TEMP). > > But your solution not install the sensor if probe fails on bad > value does not solve problem that i8k.ko is loading at time when > GPU card is turned off. > Yes, the dynamics in that situation makes it a bit difficult to handle the situation. > I think current check for installing sensor (err < 0) is enough > and when invalid value (> I8K_MAX_TEMP) is returned just do not > show this value for userspace in hwmon sysnode. > Ok with me, and agreed. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
