Messages in this thread | | | Date | Thu, 5 Jan 2023 12:43:47 -0500 | Subject | Re: [PATCH net-next v5 4/4] phy: aquantia: Determine rate adaptation support from registers | From | Sean Anderson <> |
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On 1/5/23 12:34, Vladimir Oltean wrote: > On Thu, Jan 05, 2023 at 11:21:14AM -0500, Sean Anderson wrote: >> > Your code walks through the speed_table[] of media speeds (from 10M up >> > until the max speed of the SERDES) and sees whether the PHY was >> > provisioned, for that speed, to use PAUSE rate adaptation. >> >> This is because we assume that if a phy supports rate matching for a phy >> interface mode, then it supports rate matching to all slower speeds that >> it otherwise supports. This seemed like a pretty reasonable assumption >> when I wrote the code, but it turns out that some firmwares don't abide >> by this. This is firstly a problem with the firmware (as it should be >> configured so that Linux can use the phy's features), but we have to be >> careful not to end up with an unsupported combination. > > When you say "problem with the firmware", you're referring specifically > to my example (10GBASE-R for >1G speeds, SGMII for <=1G speeds)?
Actually, I am mostly referring to cases where rate adaptation is set up to use a phy interface mode which isn't supported. In particular, Tim has a board where the phy is set up to rate adapt using 5GBASE-R (-X?), even though the host only supports 10GBASE-R.
> Why do you consider this a firmware misconfiguration? Let's say the host > supports both 10GBASE-R and SGMII, but the system designer preferred not > to use PAUSE-based rate adaptation for the speeds where native rate > adaptation was available.
This is supported, you just can't get 5G or 2.5G.
>> > If the PHY firmware uses a combination like this: 10GBASE-R/XFI for >> > media speeds of 10G, 5G, 2.5G (rate adapted), and SGMII for 1G, 100M >> > and 10M, a call to your implementation of >> > aqr107_get_rate_matching(PHY_INTERFACE_MODE_10GBASER) would return >> > RATE_MATCH_NONE, right? >> >> Correct. >> >> > So only ETHTOOL_LINK_MODE_10000baseT_Full_BIT >> > would be advertised on the media side? >> >> If the host only supports 10GBASE-R and nothing else. If the host >> supports SGMII as well, we will advertise 10G, 1G, 100M, and 10M. But >> really, this is a problem with the firmware, since if the host supports >> only 10GBASE-R, then the firmware should be set up to rate adapt to all >> speeds. > > So we lose the advertisement of 5G and 2.5G, even if the firmware is > provisioned for them via 10GBASE-R rate adaptation, right? Because when > asked "What kind of rate matching is supported for 10GBASE-R?", the > Aquantia driver will respond "None".
Correct.
>> > Shouldn't you take into consideration in your aqr107_rate_adapt_ok() >> > function only the media side link speeds for which the PHY was actually >> > *configured* to use the SERDES protocol @iface? >> >> No, because we don't know what phy interface modes are actually going to >> be used. The phy doesn't know whether e.g. the host supports both >> 10GBASE-R and SGMII or whether it only supports 10GBASE-R. With the >> current API we cannot say "I support 5G" without also saying "I support >> 1G". If you don't like this, please send a patch for an API returning >> supported speeds for a phy interface mode.
Again, this is to comply with the existing API assumptions. The current code is buggy. Of course, another way around this is to modify the API. I have chosen this route because I don't have a situation like you described. But if support for that is important to you, I encourage you to refactor things.
--Sean
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