> -----Original Message----- > From: Wood Scott-B07421 > Sent: Monday, December 22, 2014 4:33 PM > To: Medve Emilian-EMMEDVE1 > Cc: Xie Shaohui-B21989; linuxppc-dev@xxxxxxxxxxxxxxxx; > devicetree@xxxxxxxxxxxxxxx; Liberman Igal-B31950 > Subject: Re: [PATCH] [v2] power/fsl: add MDIO dt binding for FMan > > 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? [S.H] The errata only stated that it need to use a larger divider to reduce the clock Frequency, but it did not provide a suggested value, what we know is since the divider Has a limitation, then how much lower the clock frequency could be reduced has a limitation. Thanks! Shaohui > > > 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 > ��.n��������+%������w��{.n����z�{��ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f