On 2022-07-07 12:28, Vladimir Oltean wrote:
On Wed, Jul 06, 2022 at 02:25:02PM +0200, Hans Schultz wrote:
For convenience the function mv88e6xxx_g1_atu_op() has been used to
read
ATU violations, but the function has other purposes and does not
enable
the possibility to read the FID when reading ATU violations.
The FID is needed to get hold of which VID was involved in the
violation,
thus the need for future purposes to be able to read the FID.
Make no mistake, the existing code doesn't disallow reading back the
FID
during an ATU Get/Clear Violation operation, and your patch isn't
"allowing" something that wasn't disallowed.
It would only read 0 the way it worked. And I don't understand why
mv88e6xxx_g1_atu_op() writes the FID?
The documentation for the ATU FID register says that its contents is
ignored before the operation starts, and it contains the returned ATU
entry's FID after the operation completes.
So the change simply says: don't bother to write the ATU FID register
with zero, it doesn't matter what this contains. This is probably true,
but the patch needs to do what's written on the box.
Writing 0 to the ATU fID register resulted in a read giving zero of
course.
Please note that this only even matters at all for switches with
mv88e6xxx_num_databases(chip) > 256, where MV88E6352_G1_ATU_FID is a
dedicated register which this patch avoids writing. For other switches,
the FID is embedded within MV88E6XXX_G1_ATU_CTL or MV88E6XXX_G1_ATU_OP.
So _practically_, for those switches, you are still emitting the
GET_CLR_VIOLATION ATU op with a FID of 0 whether you like it or not,
and
this patch introduces a (most likely irrelevant) discrepancy between
the
access methods for various switches.
Please note that this observation is relevant for your future changes
to
read back the FID too. As I said here:
https://patchwork.kernel.org/project/netdevbpf/patch/20220524152144.40527-4-schultz.hans+netdev@xxxxxxxxx/#24912482
you can't just assume that the FID lies within the MV88E6352_G1_ATU_FID
register, just look at the way it is packed within
mv88e6xxx_g1_atu_op().
You'll need to unpack it in the same way.
So I need a new function to read the FID that mimics
mv88e6xxx_g1_atu_op()
as far as I understand?
