Russell, On Mon, Feb 18, 2019 at 10:43:02AM +0000, Russell King - ARM Linux admin wrote: > On Mon, Feb 18, 2019 at 11:26:30AM +0100, Antoine Tenart wrote: > > On Fri, Feb 15, 2019 at 05:12:24PM +0000, Russell King - ARM Linux admin > > wrote: > > > On Fri, Feb 15, 2019 at 04:32:38PM +0100, Antoine Tenart wrote: > > > > The documentation advises to set the XPCS in reset while reconfiguring > > > > the serdes lanes. This seems to be a good thing to do, but the PPv2 > > > > driver wasn't doing it. This patch fixes it. > > > > > > Hmm. That statment seems to have some ambiguity in it - we do two > > > "reconfigurations" - one may be upon initialisation, where the lane > > > is already configured for 10Gbase-KR, and we're re-initialising it > > > for the same mode. The other case is when we're switching between > > > 10Gbase-KR and SGMII, or as will be the case with 2.5G support for > > > the Alaska PHYs, 2500base-X. > > > > The configuration at the lane at boot time is dependent to the > > firmware or bootloader configuration. On the mcbin, the lane may be > > configured in 10Gbase-KR, but it could be configured in SGMII as well. > > The configuration upon initialization and the re-configuration are quite > > similar then, as we might change mode as well at boot time. > > > > You're right in that we might be re-configuring the lane for the same > > exact mode at boot time, if it was already configured in the same mode. > > > > > Does this apply to reconfiguration of the serdes lane between > > > 10Gbase-KR and slower modes? > > > > This applies only when configuring a line in a 10G mode, > > mvpp22_gop_init_10gkr isn't called otherwise. > > > > When switching to an non-10G mode we might want to put the XPCS in reset > > though, which is not done today with this patch. > > I'm merely pointing out the discrepency between the commit message and > what is actually being done. I'm not particularly concerned about what > happens at boot. > > We have four different transitions a port can go through, all of which > reconfigure the serdes lanes: > > 1. 10gkr -> 10gkr > 2. 10gkr -> non-10gkr > 3. non-10gkr -> non-10gkr > 4. non-10gkr -> 10gkr > > With this patch, XPCS is only placed into reset during the > reconfiguration for cases 1 and 4. Case 3 doesn't matter (the XPCS > should already be in reset right?) Case 2 isn't covered, and this > leaves a rather big hole. > > It seems to me that if the documentation states that the XPCS needs to > be placed in reset while the serdes is reconfigured, then what should > be happening is: > > - at boot, place the XPCS into reset. > - when we configure for 10gkr, release the reset once we've finished > configuring the serdes. > - when we configure away from 10gkr, place the XPCS back into reset > before configuring the serdes. > > Merely placing the XPCS into reset while we configure the serdes for > 10gkr doesn't seem to be "fixing" the driver to conform to your commit > message opening statement.
That's right, we should put the XPCS in reset when booting and when switching away from a 10G mode. I'll fix that in v2. Antoine -- Antoine Ténart, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
