linux-kernel - Re: [PATCH net-next v1 1/1] net: stmmac: xgmac: Enable support for multiple Flexible PPS outputs

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Date:   Thu, 26 Oct 2023 16:15:39 -0700
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Furong Xu <0x1207@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Joao Pinto <jpinto@...opsys.com>,
        Simon Horman <horms@...nel.org>
CC:     <netdev@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <xfr@...look.com>,
        <rock.xu@....com>
Subject: Re: [PATCH net-next v1 1/1] net: stmmac: xgmac: Enable support for
 multiple Flexible PPS outputs

On 10/26/2023 2:48 AM, Furong Xu wrote:
> From XGMAC Core 3.20 and later, each Flexible PPS has individual PPSEN bit
> to select Fixed mode or Flexible mode. The PPSEN must be set, or it stays
> in Fixed PPS mode by default.
> XGMAC Core prior 3.20, corresponding PPSEN bits are read-only reserved,
> always set PPSEN do not make things worse ;)
> 

Previous revisions the corresponding bits are always set, and don't get
modified by writes, so setting these bits for all hardware has no ill
effect.

In the previous code we always set BIT(4), but nwo we set BIT(4+x). This
won't affect XGMAC prior to 3.20, but corrects a mistake when
programming the newer XGMAC. Ok.

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>

The original code was added in 95eaf3cd0a90 ("net: stmmac: dwxgmac: Add
Flexible PPS support"), which landed in v5.4

It looks like XGMAC Core 3.20 support was not added until possibly
commit 669a55560e4b ("net: stmmac: Check more MAC HW features for XGMAC
Core 3.20") which appears to be new enough that its not in any official
Linux release, though it looks like it was already in net.

Perhaps this should be tagged Fixes: and sent through net, hopefully to
try and hit 6.6 or at least a stable release shortly after?

Thanks,
Jake