Re: [PATCH RFC net-next] net: stmmac: qcom-ethqos: set clk_csr

[Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>]

On Mon, Mar 30, 2026 at 01:20:18PM +0100, Russell King (Oracle) wrote:
> On Mon, Mar 30, 2026 at 01:18:56PM +0200, Konrad Dybcio wrote:
> > On 3/27/26 6:02 PM, Russell King (Oracle) wrote:
> > > The clocks for qcom-ethqos return a rate of zero as firmware manages
> > > their rate. According to hardware documentation, the clock which is
> > > fed to the slave AHB interface can crange between 50 and 100MHz.
> > 
> > FWIW this __may__ possibly differ between platforms, but I'm not sure
> > to what degree. Will there be visible impact if we e.g. have a 200 or
> > 300 MHz clock somewhere?
> 

While I had made an identical change while retesting the PCS series,
I was holding off on posting this patch for the same concern - what
if some boards fall outside the 50 - 100 MHz range.

After some digging, the AHB clock appears to operate within:
 - 50 to 100 MHz for lemans/monaco derivative boards (2500BASE-X
   interface)
 - 30 to 75 MHz for boards with an RGMII interface.

This is not exhaustive, but it covers all boards I have access to
which actually boot with the upstream kernel.

Therefore, I think using the /42 divisor should be fine as it will
ensure that MDC never goes beyond 2.5 MHz.

If a future platform exceeds this range, we could switch to something
like: plat_dat->clk_csr = data->clk_csr, with each EMAC version
selecting the appropriate divisor.

Due to some urgent work tasks, I am still finishing PCS series
testing. I will provide a t-b once done.

In the meanwhile, please feel free to add:

Reviewed-by: Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>

	Ayaan