回复: [PATCH] net:stmmac:stmmac_platform:Add snps,xpcs devicetree parsing

[Jiangfeng Ma]

> -----邮件原件-----
> 发件人: Serge Semin <fancer.lancer@xxxxxxxxx>
> 发送时间: Friday, December 8, 2023 10:28 PM
> 收件人: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>; Jiangfeng Ma <jiama@xxxxxxxxxxxx>
> 抄送: Jiangfeng Ma <jiama@xxxxxxxxxxxx>; Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>; Jose
> Abreu <joabreu@xxxxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>; Eric Dumazet
> <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>;
> Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>; Simon Horman <horms@xxxxxxxxxx>; Andrew
> Halaney <ahalaney@xxxxxxxxxx>; Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>; Shenwei
> Wang <shenwei.wang@xxxxxxx>; Johannes Zink <j.zink@xxxxxxxxxxxxxx>; Russell King (Oracle
> <rmk+kernel@xxxxxxxxxxxxxxx>; Jochen Henneberg <jh@xxxxxxxxxxxxxxxxxxxxxxxxxx>; open
> list:STMMAC ETHERNET DRIVER <netdev@xxxxxxxxxxxxxxx>; moderated list:ARM/STM32
> ARCHITECTURE <linux-stm32@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>; moderated list:ARM/STM32
> ARCHITECTURE <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; open list <linux-kernel@xxxxxxxxxxxxxxx>; James
> Li <lijames@xxxxxxxxxxxx>; Martin McKenny <mmckenny@xxxxxxxxxxxx>
> 主题: Re: [PATCH] net:stmmac:stmmac_platform:Add snps,xpcs devicetree parsing
> 
Hi Maxime, Serge
Thanks for your review!

> Hi Maxime, Jiangfeng
> 
> On Fri, Dec 08, 2023 at 09:14:08AM +0100, Maxime Chevallier wrote:
> > Hello,
> >
> > On Fri, 8 Dec 2023 07:02:19 +0000
> > Jiangfeng Ma <Jiangfeng.Ma@xxxxxxxxxxxx> wrote:
> >
> > > In order to setup xpcs, has_xpcs must be set to a non-zero value.
> > > Add new optional devicetree properties representing this.
> > >
> > > If has_xpcs is set to true, then xpcs_an_inband should preferably be
> > > consistent with it, Otherwise, some errors may occur when starting
> > > the network, For example, the phy interface that xpcs already supports,
> > > but link up fails.
> >
> > Can you elaborate on why you need this, and on which platform
> > especially ? Usually drivers for the various stmmac variants know if
> > they have XPCS or not, or can guess it based on some info such as the
> > configured PHY mode (dwmac-intel).

There is no specific platform here. I utilize the dwmcac-generic platform,
and xpcs is utilized as the MDIO device or it can be seen as a C45 PHY.
While it's sometimes possible to deduce the presence of xpcs based on information
such as the phy mode (dwmac-intel), this is not always a definitive indicator.
For instance, the support of SGMII by XPCS doesn't imply
that all SGMII-supporting PHYs include XPCS. But as Serge mentioned, using pcs-handle,
or pcs-handle-name might be a more effective approach.
> >
> > Besides that, there are a few issues with your submission. If DT is the
> > way to go (and I don't say it is), you would also need to update the
> > bindings to document that property.
> >
> > > The types of has_xpcs and xpcs_an_inband are unsigned int,
> > > and generally used as flags. So it may be more reasonable to set them to
> > > bool type. This can also be confirmed from the type of @ovr_an_inband.
> >
> > And this part would go into a separate patch.
Sorry for this issue, I will create the patch separately later.
> 
> In addition to what Maxime already said having DT-bindings adjusted to
> fit to the pattern implemented in the software part is a wrong way to
> go. The best choice in this case is to add the DW XPCS DT-node to the
> DW MAC MDIO/MI bus and then use the "pcs-handle" to inform the MAC
> (mainly it's driver) of what PCS-device is actually attached to it.
> The series I submitted on this week is exactly about that:
> https://urldefense.com/v3/__https://lore.kernel.org/netdev/20231205103559.9605-1-fancer.lancer@g
> mail.com/__;!!A4F2R9G_pg!Y6R3WZWHeBdrkZklbqrAQARbHnQ-g_Tbb6r5IqcsSHMQ_l4rOzLLgZvLPl6YP
> BYferbjrbjZA6_XvSSSvkV35eo2jWPz$
> I guess I'll need about a month or so to settle all the comments, but
> the solution implemented there will be better than this one really.
>
Yes, I agree that binding the xpcs via the "pcs-handle" DT firmware node 
is a better way. but the current method of binding xpcs through scanning 
addresses still relies on mdio_bus_data->has_xpcs. 
The 16th patch in your patchset also mentions the difficulty of 
obtaining has_xpcs. Therefore, can we add parsing of pcs-handle-names 
in the platform to determine if the xpcs exists, like this:

if (plat->mdio_bus_data) {
	rc = of_property_match_string(np, "pcs-handle-names", "dw-xpcs");
	if (rc >= 0) {
		plat->mdio_bus_data->has_xpcs = true;
		plat->mdio_bus_data->xpcs_an_inband = true;
	}
}

Thanks,
Jiangfeng

> -Serge(y)
> 
> >
> > Thanks,
> >
> > Maxime
> >