netdev - Re: [PATCH v4] net: macb: Fix several edge cases in validate

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Message-ID: <7022cd00-e863-d0ed-3a48-8fe9d48968e2@microchip.com>
Date:   Wed, 27 Oct 2021 07:02:11 +0000
From:   <Nicolas.Ferre@...rochip.com>
To:     <sean.anderson@...o.com>, <linux@...linux.org.uk>
CC:     <netdev@...r.kernel.org>, <davem@...emloft.net>, <kuba@...nel.org>,
        <Claudiu.Beznea@...rochip.com>, <atenart@...nel.org>,
        <pthombar@...ence.com>, <mparab@...ence.com>
Subject: Re: [PATCH v4] net: macb: Fix several edge cases in validate

Sean, Russell,

On 26/10/2021 at 20:52, Sean Anderson wrote:
>>
>> Going back to the first point I mentioned above, how much should we
>> take from these documents as actually being correct? Should we not
>> assume anything, but instead just experiment with the hardware and
>> see what works.
>> For example, are the two speed bits in the PCS control register
>> really read-only when in Cisco SGMII mode, or can they be changed -
>> and if they can be changed, does that have an effect on the ethernet
>> link?
> Keep in mind that it is not only Zynq(MP) parts with have GEMs, but
> several other SoCs as well. I have not reviewed their datasheets (except
> for SiFive's which just say "go read the Linux driver"). It is possible
> that other SoCs may not have these limitations. So any experimental
> program will need to also experiment with e.g. sama.

Claudiu and myself can certainly help in reviewing and testing on 
Microchip devices. The limitation that I see is that we only have 10/100 
and 1000 speeds implemented in our SoC with limited number of link types 
covered (MII, RMII, GMII and RGMII).

Our datasheets including different variants of MACB and GEM can give 
some information:
MACB example in: 
http://ww1.microchip.com/downloads/en/DeviceDoc/SAM9X60-Data-Sheet-DS60001579A.pdf

GEM example at 10/100 in: 
https://www.microchip.com/content/dam/mchp/documents/MPU32/ProductDocuments/DataSheets/SAMA5D2-Series-Data-sheet-ds60001476G.pdf

GEM example with 10/100/1000 in: 
https://www.microchip.com/content/dam/mchp/documents/MPU32/ProductDocuments/DataSheets/SAMA5D3-Series-Data-sheet-DS60001609b.pdf

We can also explore some of the design and configuration registers (DCFGn).

> Perhaps someone from cadence could comment on what is actually supported
> by gem/macb?

That could be good as well.

Best regards,
   Nicolas

-- 
Nicolas Ferre