Re: [PATCH RFC net-next 3/3] net: dsa: add basic initial driver for MxL862xx switches

[Andrew Lunn <andrew@lunn.ch>]

On Fri, Dec 12, 2025 at 04:49:47PM +0000, Daniel Golle wrote:
> Hi Andrew,
> 
> On Wed, Dec 10, 2025 at 07:56:13PM +0100, Andrew Lunn wrote:
> > > > > +	if (result < 0) {
> > > > > +		ret = result;
> > > > > +		goto out;
> > > > > +	}
> > > > 
> > > > If i'm reading mxl862xx_send_cmd() correct, result is the value of a
> > > > register. It seems unlikely this is a Linux error code?
> > > 
> > > Only someone with insights into the use of error codes by the uC
> > > firmware can really answer that. However, as also Russell pointed out,
> > > the whole use of s16 here with negative values being interpreted as
> > > errors is fishy here, because in the end this is also used to read
> > > registers from external MDIO connected PHYs which may return arbitrary
> > > 16-bit values...
> > > Someone in MaxLinear will need to clarify here.
> > 
> > It looks wrong, and since different architectures use different error
> > code values, it is hard to get right. I would suggest you just return
> > EPROTO or EIO and add a netdev_err() to print the value of result.
> 
> MaxLinear folks got back to me. So the error codes returned by the firmware
> are basically based on Zephyr's errno.h which seems to be a copy of a BSD
> header, see
> 
> https://github.com/zephyrproject-rtos/zephyr/blob/main/lib/libc/minimal/include/errno.h
> 
> So the best would probably be to modify and include that header with the
> driver, together with a function translating the error codes to what ever
> is defined in uapi/asm/errno.h for the architecture we are building for.
> 
> They also told me that (obviously) not all error codes are currently
> used by the firmware, but the best would be to just catch all the possible
> error codes and translate Zephyr libc -> Linux kernel.

That all sounds way too complex. We don't expect errors do we? So
print the raw value, add a comment about how to manually translate the
number to something potentially meaningful, and return -EIO.

	  Andrew