netdev - Re: [QUERY] : STMMAC Clocks

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Message-ID: <Z8LkPQ-w_jyXriFp@shell.armlinux.org.uk>
Date: Sat, 1 Mar 2025 10:41:01 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	Jose Abreu <joabreu@...opsys.com>, netdev <netdev@...r.kernel.org>
Subject: Re: [QUERY] : STMMAC Clocks

On Sat, Mar 01, 2025 at 12:38:04AM +0100, Andrew Lunn wrote:
> On Fri, Feb 28, 2025 at 09:51:15PM +0000, Lad, Prabhakar wrote:
> > Hi All,
> > 
> > I am bit confused related clocks naming in with respect to STMMAC driver,
> > 
> > We have the below clocks in the binding doc:
> > - stmmaceth
> > - pclk
> > - ptp_ref
> > 
> > But there isn't any description for this. Based on this patch [0]
> > which isn't in mainline we have,
> > - stmmaceth - system clock
> > - pclk - CSR clock
> > - ptp_ref - PTP reference clock.
> > 
> > [0] https://patches.linaro.org/project/netdev/patch/20210208135609.7685-23-Sergey.Semin@baikalelectronics.ru/
> > 
> > Can somebody please clarify on the above as I am planning to add a
> > platform which supports the below clocks:
> > - CSR clock
> > - AXI system clock
> > - Tx & Tx-180
> > - Rx & Rx-180
> 
> Please take a look at the recent patches to stmmac for clock handling,
> in particular the clocks used for RGMII
> 
> For the meaning of the clocks, you need to look at the vendors binding
> document. Vendors tend to call the clocks whatever they want, rather
> than have one consistent naming between vendors. The IP might be
> licensed, but each vendor integrates it differently, inventing their
> own clock names. It might of helped if Synopsis had requested in there
> databook what each clock was called, so there was some consistency,
> but this does not appear to of happened.

Part of the problem is that vendors can place clock muxes and gates
and divisors around the Synopsys block, where some muxes/divisors can
be controlled by signals output by the Synopsys block (and thus are
hidden from software). This is especially true of the pair of clk_tx_i
and pair of clk_rx_i clocks.

Thus, the clocks that are visible may be functionally different from
the Synopsys defined clocks.

However, I think that we should push to standardise on the Synopsys
named clock names where they exist (essentially optional) and then
allow platform specific clocks where they're buried out of view in
the way I describe above.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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