> >> > + /* read only dropped counters when link is not up */ > >> > + if (p->link_just_down) > >> > + p->link_just_down = 0; > >> > + else if (!p->phydev.link) > >> > + mib->cnt_ptr = dev->reg_mib_cnt; > >> > >> This link_just_down stuff is not clear at all. Why can the drop > >> counters not be read when the link is up? > > > >All of the MIB counters, except some that may be marked by driver, do > >not get updated when the link is down, so it is a waste of time to read > >them. > > Can you use netif_running() to determine that condition? Maintaining your > own set of variables when the PHY state machine should already determine > the link state sounds redundant if not error prone. >
The driver can store the PHY device pointer passed to it when the port is enabled. But I am a little worried that pointer can be changed or completely gone as it is out of control of the driver. > >My intention is the driver eventually reads the MIB counters at least > >every second or faster so that the ethtool API called to show MIB > >counters gets them from memory rather than starting a read operation. > >For now that API is called from user space with the ethtool utility, so > >it may not be called too often and too fast. But theoretically that > >API can be called from a program continually. > > > >For simple switches that do not need to do anything special the MIB > >read operation does not cause any issue except CPU load, for more > >complicate switches that need to do some background operations too many > >read operation can affect some critical functions. > > Some switches have a MIB autocast feature taking a snapshot which AFAIR is > internally implemented as a fast read register with no contention on other > registers internally, do you have something similar? There is no such function in the switch. Every MIB counter read has to go through a single SPI transfer using indirect access. There are no table-like stored values that a single SPI transfer can retrieve all. For i2C the access is even slower, but then I do not expect this access mechanism is used when the switch can do more complex things.
