Messages in this thread | | | Date | Thu, 30 Jun 2022 23:00:37 +0200 | From | Michael Walle <> | Subject | Re: fwnode_for_each_child_node() and OF backend discrepancy |
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Am 2022-06-30 22:16, schrieb Horatiu Vultur: > The 06/28/2022 23:07, Michael Walle wrote: >> EXTERNAL EMAIL: Do not click links or open attachments unless you know >> the content is safe >> >> Am 2022-06-28 22:52, schrieb Horatiu Vultur: >> > The 06/28/2022 22:28, Andy Shevchenko wrote: >> > > EXTERNAL EMAIL: Do not click links or open attachments unless you know >> > > the content is safe >> > > >> > > On Tue, Jun 28, 2022 at 5:17 PM Krzysztof Kozlowski >> > > <krzysztof.kozlowski@linaro.org> wrote: >> > > > On 28/06/2022 17:09, Michael Walle wrote: >> > >> > Hi, >> > >> > Sorry for joint this late. >> > >> > > >> > > ... >> > > >> > > > > Mh. Assume a SoC with an integrated ethernet switch. Some ports >> > > > > are externally connected, some don't. I'd think they should be disabled, >> > > > > no? Until now, all bindings I know, treat them as disabled. But OTOH >> > > > > you still need to do some configurations on them, like disable port >> > > > > forwarding, disable them or whatever. So the hardware is present, but >> > > > > it is not connected to anything. >> > > > >> > > > I see your point and the meaning is okay... except that drivers don't >> > > > touch disabled nodes. If a device (with some address space) is disabled, >> > > > you do not write there "please be power off". Here the case is a bit >> > > > different, because I think ports do not have their own address space. >> > > > Yet it contradicts the logic - something is disabled in DT and you >> > > > expect to perform actual operations on it. >> > > >> > > You beat me up to this comment, I also see a contradiction of what >> > > "disabled" means in your, Michael, case and what it should be. >> > > >> > > If you need to perform an operation on some piece of HW, it has not to >> > > be disabled. >> > > >> > > Or, you may deduce them by knowing how many ports in hardware (this is >> > > usually done not by counting the nodes, but by a property) and do >> > > whatever you want on ones, you have not listed (by port_num) in the >> > > array of parsed children. >> > >> > It is not possible to have a defined for the MAX number of ports that >> > supported by lan966x. Which is 8. And assigned that define to >> > num_phys_ports instead of counting the entries in DT? >> >> You mean also for the lan9662? I'm pretty sure that doesn't >> work. Have a look where num_phys_ports is used. One random >> example: >> https://elixir.bootlin.com/linux/latest/source/drivers/net/ethernet/microchip/lan966x/lan966x_main.c#L874 >> >> So if your switch only has 4 ports, then I'd guess you'll >> access a non-existing register. > > Underneath lan662 and lan668 is the same chip. The HW people disable > some ports/features on each platform but from what I know you will > still > be able to access the registers.
I noticed that there are still 8 ports in the register description and assumed that it was wrong [1]. But ok, that makes sense in some way. OTOH that means, we cannot do the guesswork Vladimir proposed.
-michael
[1] https://microchip-ung.github.io/lan9662_reginfo/reginfo_LAN9662.html
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