linux-kernel - Re: [PATCH 1/4] net: stmmac: s32: use the syscon interface PHY_INTF_SEL

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Message-ID: <aS3GzJljbfp2xJmW@shell.armlinux.org.uk>
Date: Mon, 1 Dec 2025 16:48:12 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Jan Petrous <jan.petrous@....nxp.com>, s32@....com,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-s32@...aro.org
Subject: Re: [PATCH 1/4] net: stmmac: s32: use the syscon interface
 PHY_INTF_SEL_RGMII

On Mon, Dec 01, 2025 at 04:08:20PM +0300, Dan Carpenter wrote:
> On the s32 chipset the GMAC_0_CTRL_STS register is in GPR region.
> Originally, accessing this register was done in a sort of ad-hoc way,
> but we want to use the syscon interface to do it.
> 
> This is a little bit uglier because we to maintain backwards compatibility
> to the old device trees so we have to support both ways to access this
> register.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  .../net/ethernet/stmicro/stmmac/dwmac-s32.c   | 23 +++++++++++++++----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> index 5a485ee98fa7..20de761b7d28 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-s32.c
> @@ -11,12 +11,14 @@
>  #include <linux/device.h>
>  #include <linux/ethtool.h>
>  #include <linux/io.h>
> +#include <linux/mfd/syscon.h>
>  #include <linux/module.h>
>  #include <linux/of_mdio.h>
>  #include <linux/of_address.h>
>  #include <linux/phy.h>
>  #include <linux/phylink.h>
>  #include <linux/platform_device.h>
> +#include <linux/regmap.h>
>  #include <linux/stmmac.h>
>  
>  #include "stmmac_platform.h"
> @@ -32,6 +34,8 @@
>  struct s32_priv_data {
>  	void __iomem *ioaddr;
>  	void __iomem *ctrl_sts;
> +	struct regmap *sts_regmap;
> +	unsigned int sts_offset;
>  	struct device *dev;
>  	phy_interface_t *intf_mode;
>  	struct clk *tx_clk;
> @@ -40,7 +44,10 @@ struct s32_priv_data {
>  
>  static int s32_gmac_write_phy_intf_select(struct s32_priv_data *gmac)
>  {
> -	writel(S32_PHY_INTF_SEL_RGMII, gmac->ctrl_sts);
> +	if (gmac->ctrl_sts)
> +		writel(S32_PHY_INTF_SEL_RGMII, gmac->ctrl_sts);
> +	else
> +		regmap_write(gmac->sts_regmap, gmac->sts_offset, PHY_INTF_SEL_RGMII);

Sorry, but even if that regmap_write() is targetting the exact same
register, these are not identical.

S32_PHY_INTF_SEL_RGMII, which is a S32-specific value, takes the value 2.
PHY_INTF_SEL_RGMII is the dwmac specific value, and takes the value 1.

If this targets the same register, then by writing PHY_INTF_SEL_RGMII,
you are in effect writing the equivalent of S32_PHY_INTF_SEL_SGMII to
it. This seems like a bug.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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