Messages in this thread |  | | Date | Wed, 18 Feb 2015 09:40:22 +0000 | From | Stathis Voukelatos <> | Subject | Re: [PATCH v2 1/3] Ethernet packet sniffer: Device tree binding and vendor prefix |
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On 17/02/15 17:30, Mark Rutland wrote:
>> It is the frequency of the timestamp values supplied to the sniffer >> module. It is used by the driver to convert to nanoseconds. >> I was trying to be somewhat generic here and not assume that it >> is necessarily the same as the 'tstamp' clock below, in which case we >> could indeed obtain it using the common clock framework. > > In what cases would it _not_ be the same? From your description this is > that clock, no? >
Counters can often have a divider applied to their input clock and therefore run at a scaled down frequency. This is not the case in the first SoC where the sniffer is used, so for simplicity I can modify as you suggest and remove that field from the DT.
>> Most networking driver use hard-coded values for that, but in my case >> I did not want to assume a certain fixed clock frequency. I will remove >> it from the DT and generate it dynamically. There is a kernel function >> clocks_calc_mult_shift() to do it but unfortunately it is not exported, >> so I guess I will need to replicate the code. > > Or submit a patch exporting it, along with the rationale for doing so? >
Will do that.
>> Yes, but the sniffer module is hard-wired to a certain Ethernet Mii >> interface. We can add an entry to tie it to an Ethernet controller, but >> apart of a sanity check I am not sure what else the S/W can do. > > Fundamentally, the use-case for this is monitoring an ethernet > interface. So regardless of which kernel framework this plumbs into, > there needs to be a way to go from ethN to whatever this is exposed as. > > Exposing a completely separate interface makes no sense. Singleton stuff > like that inevitably gets broken as someone later builds a board with > multiple instances of some similar IP block. > > So I would imagine that either the link between interface and monitoring > interface would be described somewhere in the filesystem, or there'd be > a syscall/ioctl/whatever to go from an interface to the appropriate > monitoring interface. > > That all depends on exactly how this gets exposed in the end, however. >
After the first version of the patch was submitted, the feedback from the netdev list was to expose it as a network interface as this would allow it to be accessed by standard user space monitoring tools. It definitely makes sense to link it to the associated ethernet netdev, but I am not sure if there is a framework in the kernel to do it at the driver level?
> Thanks, > Mark. > --
Thank you, Stathis
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