Hello Scott, On 12/22/2014 02:32 AM, Scott Wood wrote: > On Mon, 2014-12-22 at 02:20 -0600, Emil Medve wrote: >> Hello Shao-Hui, >> >> >> On 12/21/2014 08:31 PM, Xie Shaohui-B21989 wrote: >>>> On Fri, 2014-12-19 at 01:23 -0600, Xie Shaohui-B21989 wrote: >>>>>> -----Original Message----- >>>>>> From: Wood Scott-B07421 >>>>>> Sent: Friday, December 19, 2014 6:01 AM >>>>>> To: Xie Shaohui-B21989 >>>>>> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; Medve >>>>>> Emilian- EMMEDVE1; Liberman Igal-B31950 >>>>>> Subject: Re: [PATCH] [v2] power/fsl: add MDIO dt binding for FMan >>>>>> >>>>>> On Thu, 2014-12-18 at 06:53 -0600, Xie Shaohui-B21989 wrote: >>>>>>> Ping. >>>>>>> >>>>>>> Best Regards, >>>>>>> Shaohui Xie >>>>>> >>>>>> I can't put patches in my -next until the merge window closes. >>>>>> >>>>>>>>>> +EXAMPLE >>>>>>>>>> + >>>>>>>>>> +Example for FMan v2 external MDIO: >>>>>>>>>> + >>>>>>>>>> +mdio@f1000 { >>>>>>>>>> + compatible = "fsl,fman-xmdio"; >>>>>>>>>> + reg = <0xf1000 0x1000>; >>>>>>>>>> + bus-frequency = <20000>; >>>>>>>>>> +}; >>>>>>>>> >>>>>>>>> So the bus frequency is only 20 KHz? Or is the unit supposed >>>>>>>>> to be something other than Hz? >>>>>>>> [S.H] it's only an example, it could be different on real SoCs, >>>>>>>> but they always lower than the standard one, The standard one is >>>>>>>> 2.5MHz, I have >>>>>> to use Hz for it. >>>>>> >>>>>> Is there any SoC for which 20 kHz is the right frequency? I just >>>>>> want to make sure the example is realistic. >>>>> [S.H] the clock divider has a limitation that the MAX value it can get >>>>> on Fman v2 is 255 (0xff, 8 bits), On Fman v3 is 511(0x1ff, 9 bits). >>>>> >>>>> So the lowest frequency on Fman v2 is: Fman_clock / (2 * 255), On Fman >>>>> v3 is: Fman_clock / ((2 * 511) + 1). >>>>> >>>>> Take default Fman frequency setting from SDK1.7 as example, the lowest >>>>> clock used for Fman v2 is 581MHz, The lowest clock for Fman v3 is 600MHz. >>>>> >>>>> Then the lowest bus frequency can get is: >>>>> Fman v2: ~1140KHz >>>>> Fman v3: ~587KHz >>>>> >>>>> 20KHz is not practice, we don't have a suggested value in errata document. >>>>> For this example, should I post a new version with a value like 1200KHz? >>>> >>>> This is different from how you described the problem before. If the limitation >>>> is on the divider, rather than the absolute bus frequency, then specifiy the max >>>> divider. Or better, since according to the above this correlates with fman >>>> version, just have the driver know what the max divider is for each fman version. >>> [S.H] The problem is not the divider has limitation, the problem is a different bus frequency >>> Is needed which is lower than the standard, but due to the divider limitation, the lowest >>> bus frequency also has limitation. i.e. we need to use the divider to get a lower frequency, >>> but how much lower the value could be is restricted by the divider limitation. > > This is difficult to follow -- are you saying the erratum requires a > speed that is not achievable? > >> For the purpose of an example in the binding document, I suggest we just >> stick with the IEEE standard frequency. > > The whole reason for this property existing in the device tree is > non-standard frequencies. While the standard claims 2.5 MHz, most MDIO controllers and PHY devices support frequencies well beyond the standard. Specifying a lower then the standard frequency for the benefit of some errata is just one side of this property >> We can continue this conversation about errata handling when we submit >> the code relevant to this binding (and the FMan v3 support) > > It affects the binding, so let's discuss it now please. I think this specific (unpublished yet) errata has less bearing on the binding then you might believe. This is mostly about providing a common/default frequency supported by all the devices on some board Anyway, the above thread about bits and lowest frequency limitation(s) is not really a problem/limitation. The range of frequencies (dividers) supported by both controller versions in all the supported SoC(s) allows responding to this (FMan v3 only) errata just fine Cheers, -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html