Hi all,

On Sep. Friday 25 (39) 11:03 AM, Vivien Didelot wrote:

On Sep. Thursday 24 (39) 10:55 PM, David Miller wrote:

quoted

From: Scott Feldman <redacted>
Date: Thu, 24 Sep 2015 22:29:43 -0700

quoted

I'd rather keep 2-phase not optional, or at least make it some what of
a pain for drivers to opt-out of 2-phase.  Forcing the driver to see
both phases means the driver needs to put some code to skip phase 1
(and hopefully has some persistent comment explaining why its being
skipped).  Something like:

/* I'm skipping phase 1 prepare for this operation.  I have infinite hardware
 * resources and I'm not setting any persistent state in the driver or device
 * and I don't need any dynamic resources from the kernel, so its impossible
 * for me to fail phase 2 commit.  Nothing to prepare, sorry.
 */

I agree with Scott here.

If you can opt out of something, you can not think about it and thus
more likely get it wrong.

I can just see a driver not implementing prepare at all and then doing
stupid things in commit when they hit some resource limit or whatever,
rather than taking care of such issues in prepare.

OK, I have no experience with stacked devices nor what it actually looks
like, but I understand that it is a redundant setup where it makes sense
to ensure that an operation is feasible before programming the hardware.

I agree with both of you on imposing switchdev drivers such notion.

I was confused with the rtnl lock (from bridge netlink requests) which
seemed to limit a lot the usage of this prepare phase.

I don't know the batch mode neither, but I can think about a potentially
powerful usage of the prepare phase in Marvell switches (or any basic
home router switches), please tell me if the following is feasible:

Every hardware VLANs I know of are programmed with all port membership
in one shot. This is not feasible today with the bridge command. If I
could bundle in one request the equivalent of ("VID 100: 0u 1u 5t"):

    bridge vlan add master dev swp0 vid 100 pvid untagged
    bridge vlan add master dev swp1 vid 100 pvid untagged
    bridge vlan add master dev swp5 vid 100 # cpu

In such case the prepare phase could be great to allocate and populate a
VLAN entry structure (i.e. struct mv88e6xxx_vtu_stu_entry) before
programming the hardware *just once*. Is that doable?

May I get answers for this? I'd need that in order to suggest a next
step for the prepare phase in DSA drivers.

Thanks,
-v