Messages in this thread | | | Date | Fri, 19 Dec 2014 10:33:43 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH 2/3] i8k: Autodetect maximal fan speed and fan RPM multiplier |
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On Thu, Dec 18, 2014 at 12:13:35PM +0100, Pali Rohár wrote: > On Wednesday 10 December 2014 15:08:11 Guenter Roeck wrote: > > On 12/10/2014 03:50 AM, Pali Rohár wrote: > > > On Tuesday 09 December 2014 23:42:08 Guenter Roeck wrote: > > >> On Tue, Dec 09, 2014 at 09:23:22PM +0100, Pali Rohár wrote: > > >>> On Tuesday 09 December 2014 21:20:23 Guenter Roeck wrote: > > >>>> On Tue, Dec 09, 2014 at 09:07:00PM +0100, Pali Rohár > wrote: > > >>>>> This patch adds new function i8k_get_fan_nominal_rpm() > > >>>>> for doing SMM call which will return nominal fan RPM > > >>>>> for specified fan speed. It returns nominal RPM value > > >>>>> at which fan operate when speed is set. It looks like > > >>>>> RPM value is not accurate, but still provides very > > >>>>> useful information. > > >>>>> > > >>>>> First it can be used to validate if certain fan speed > > >>>>> could be accepted by SMM for setting fan speed and we > > >>>>> can use this routine to detect maximal fan speed. > > >>>>> > > >>>>> Second it returns RPM value, so we can check if value > > >>>>> looks correct with multiplier 30 or multiplier 1 (until > > >>>>> now only these two multiplier was used). If RPM value > > >>>>> with multiplier 30 is too high, then multiplier 1 is > > >>>>> used. > > >>>>> > > >>>>> In case when SMM reports that new function is not > > >>>>> supported we will fallback to old hardcoded values. > > >>>>> Maximal fan speed would be 2 and RPM multiplier 30. > > >>>>> > > >>>>> Signed-off-by: Pali Rohár <pali.rohar@gmail.com> > > >>>>> --- > > >>>>> I tested this patch only on my Dell Latitude E6440 and > > >>>>> autodetection worked fine Before appying this patch it > > >>>>> should be tested on some other dell machines too but if > > >>>>> machine does not support i8k_get_fan_nominal_rpm() > > >>>>> driver should fallback to old values. So patch should > > >>>>> be without regressions. > > >>>> > > >>>> It looks like many of your error checks are unnecessary. > > >>>> Why did you add those ? > > >>>> > > >>>> Please refrain from adding unnecessary code. > > >>>> > > >>>> Guenter > > >>> > > >>> Which error checks do you mean? > > >> > > >> There are several you added. I noticed the ones around > > >> 'index', which would only be hit on coding errors. At that > > >> point I stopped looking further and did not verify which of > > >> the other added error checks are unnecessary as well. > > >> > > >> A quick additional check reveals that the fan variable > > >> range check in i8k_get_fan_nominal_rpm is completely > > >> unnecessary - if the range was wrong, the calling code > > >> would fail as well, since you unconditionally write into > > >> an array indexed by the very same variable. Given the > > >> simplicity of the calling code, it can even be > > >> mathematically proven that the error condition you are > > >> checking can never happen. > > >> > > >> With that I really stopped looking further. > > >> > > >> Guenter > > > > > > Should I remove those access out-of-array checks? > > > > If you want me to look into it further. In general, I don't > > accept code like this, since it increases kernel size for no > > good reason. It also makes it more difficult to find _real_ > > problems in the code since it distracts from seeing those. > > > > Guenter > > Ok, I will rework this patch and drop that first cosmetic. > Fine, but as mentioned before I still dislike unnecessary value range checks.
Guenter
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