Messages in this thread | | | Date | Fri, 10 Feb 2023 13:35:02 +0100 | Subject | Re: [PATCH v2 03/11] dt-bindings: arm: mediatek: add 'mediatek,pn_swap' property | From | Krzysztof Kozlowski <> |
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On 10/02/2023 13:23, Russell King (Oracle) wrote: > On Fri, Feb 10, 2023 at 10:34:17AM +0000, Russell King (Oracle) wrote: >> On Thu, Feb 09, 2023 at 12:30:27PM +0100, Krzysztof Kozlowski wrote: >>> On 08/02/2023 23:30, Daniel Golle wrote: >>>> Hm, none of the current PCS (or PHY) drivers are represented by a >>>> syscon node... (and maybe that's the mistake in first place?) >>> >>> Yes. >> >> Nos, it isn't. > > To expand on this - I have no idea why you consider it a mistake that > apparently all PCS aren't represented by a syscon node. > > PCS is a sub-block in an ethernet system, just the same as a MAC is a > sub-block. PCS can appear in several locations of an ethernet system, > but are generally found either side of a serial ethernet link such > as 1000base-X, SGMII, USXGMII, 10Gbase-R etc. > > So, one can find PCS within an ethernet PHY - and there may be one > facing the MAC connection, and there will be another facing the media. > We generally do not need to separate these PCS from the PHY itself > because we view the PHY as one whole device. > > The optional PCS on the MAC side of the link is something that we > need to know about, because this has to be configured to talk to the > PHY, or to configure and obtain negotiation results from in the case of > fibre links. > > PCS on the MAC side are not a system level device, they are very much a > specific piece of ethernet hardware in the same way that the MAC is, > and we don't represent the MAC as a syscon node. There is no reason > to do so with PCS. > > These PCS on the MAC side tend to be accessed via direct MMIO accesses, > or over a MDIO bus. > > There's other blocks in the IEEE 802.3 ethernet layering, such as the > PMA/PMD module (which for the MAC side we tend to model with the > drivers/phy layer) - but again, these also appear in ethernet PHYs > in order to produce the electrical signals for e.g. twisted pair > ethernet. > > So, to effectively state that you consider that PCS should always be > represented as a syscon node is rather naieve, and really as a DT > reviewer you should not be making such decisions, but soliciting > opinions from those who know this subject area in detail _whether_ > they are some kind of system controller before making such a > decision.
Daniel switched to private emails, so unfortunately our talk is not visible here, nevertheless thanks for the feedback. Much appreciated!
Best regards, Krzysztof
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