linux-kernel - Re: [PATCH net-next v3 2/2] net:dsa:microchip: add property to select internal RMII reference clock

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Date:   Thu, 19 Oct 2023 19:54:09 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Ante Knezic <ante.knezic@...mholz.de>
Cc:     netdev@...r.kernel.org, woojung.huh@...rochip.com, andrew@...n.ch,
        f.fainelli@...il.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        marex@...x.de, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v3 2/2] net:dsa:microchip: add property to
 select internal RMII reference clock

On Wed, Oct 18, 2023 at 11:24:14AM +0200, Ante Knezic wrote:
> Microchip KSZ8863/KSZ8873 have the ability to select between internal
> and external RMII reference clock. By default, reference clock
> needs to be provided via REFCLKI_3 pin. If required, device can be
> setup to provide RMII clock internally so that REFCLKI_3 pin can be
> left unconnected.
> Add a new "microchip,rmii-clk-internal" property which will set
> RMII clock reference to internal. If property is not set, reference
> clock needs to be provided externally.
> 
> Signed-off-by: Ante Knezic <ante.knezic@...mholz.de>
> ---
>  drivers/net/dsa/microchip/ksz8795.c     | 10 +++++++++-
>  drivers/net/dsa/microchip/ksz8795_reg.h |  3 +++
>  drivers/net/dsa/microchip/ksz_common.h  |  1 +
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c
> index 91aba470fb2f..b50ad9552c65 100644
> --- a/drivers/net/dsa/microchip/ksz8795.c
> +++ b/drivers/net/dsa/microchip/ksz8795.c
> @@ -1312,8 +1312,16 @@ void ksz8_port_setup(struct ksz_device *dev, int port, bool cpu_port)
>  	ksz_port_cfg(dev, port, P_PRIO_CTRL, PORT_802_1P_ENABLE, true);
>  
>  	if (cpu_port) {
> -		if (!ksz_is_ksz88x3(dev))
> +		if (!ksz_is_ksz88x3(dev)) {
>  			ksz8795_cpu_interface_select(dev, port);
> +		} else {
> +			dev->rmii_clk_internal = of_property_read_bool(dev->dev->of_node,
> +								       "microchip,rmii-clk-internal");
> +
> +			ksz_cfg(dev, KSZ88X3_REG_FVID_AND_HOST_MODE,
> +				KSZ88X3_PORT3_RMII_CLK_INTERNAL,
> +				dev->rmii_clk_internal);

Odd code placement, and it looks too crammed/shifted to the right due to indentation.

The calling pattern is as follows: ksz8_port_setup() has 2 callers.

One is from
ds->ops->port_setup()
-> ksz_port_setup()
   -> filters out everything except user ports
   -> dev->dev_ops->port_setup()
      -> ksz8_port_setup()

and the other is from
ds->ops->setup() // switch-wide
-> dev->dev_ops->config_cpu_port()
   -> ksz8_config_cpu_port()
      -> ksz8_port_setup()

So user ports and CPU ports meet at ksz8_port_setup() from different
call paths, but I think it's strange to continue this coding pattern for
port stuff that's not common between user ports and CPU ports. For that
reason, the placement of the existing ksz8795_cpu_interface_select() is
also weird, when it could have been directly placed under
ksz8_config_cpu_port(), and it would have not confusingly shared a code
path with user ports.

Could you please add a dedicated ksz88x3_config_rmii_clk(), called
directly from ksz8_config_cpu_port()? It can have this as first step:

	if (!ksz_is_ksz88x3(dev))
		return 0;

and then the rest of the code can have a single level of indentation,
which would look much more natural.

> +		}
>  
>  		member = dsa_user_ports(ds);
>  	} else {
>