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. > 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. -Scott -- 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