Re: [PATCH v1 2/2] net: stmmac: Add NPCM support

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Tomer Maimon <tmaimon77@gmail.com>
Cc: alexandre.torgue@foss.st.com, tali.perry1@gmail.com,
	edumazet@google.com, krzysztof.kozlowski+dt@linaro.org,
	linux-stm32@st-md-mailman.stormreply.com,
	benjaminfair@google.com, openbmc@lists.ozlabs.org,
	joabreu@synopsys.com, joel@jms.id.au, devicetree@vger.kernel.org,
	j.neuschaefer@gmx.net, robh+dt@kernel.org,
	peppe.cavallaro@st.com, linux-arm-kernel@lists.infradead.org,
	avifishman70@gmail.com, venture@google.com,
	linux-kernel@vger.kernel.org, mcoquelin.stm32@gmail.com,
	netdev@vger.kernel.org, davem@davemloft.net
Subject: Re: [PATCH v1 2/2] net: stmmac: Add NPCM support
Date: Tue, 21 Nov 2023 15:45:11 +0000	[thread overview]
Message-ID: <ZVzQh9ykusyknGgP@shell.armlinux.org.uk> (raw)
In-Reply-To: <20231121151733.2015384-3-tmaimon77@gmail.com>

On Tue, Nov 21, 2023 at 05:17:33PM +0200, Tomer Maimon wrote:
> Add Nuvoton NPCM BMC SoCs support to STMMAC dwmac driver.
> 
> And modify MAINTAINERS to add a new F: entry for this driver.
> 
> Signed-off-by: Tomer Maimon <tmaimon77@gmail.com>

A few comments on this...

> +#define IND_AC_BA_REG		0x1FE
> +#define SR_MII_CTRL		0x3E0000
> +
> +#define PCS_SR_MII_CTRL_REG	0x0
> +#define PCS_SPEED_SELECT6	BIT(6)
> +#define PCS_AN_ENABLE		BIT(12)
> +#define PCS_SPEED_SELECT13	BIT(13)
> +#define PCS_RST			BIT(15)

include/uapi/linux/mii.h:

#define BMCR_SPEED1000          0x0040  /* MSB of Speed (1000)         */
#define BMCR_ANENABLE           0x1000  /* Enable auto negotiation     */
#define BMCR_SPEED100           0x2000  /* Select 100Mbps              */
#define BMCR_RESET              0x8000  /* Reset to default state      */

Look familiar? Maybe use the standard definitions for a standardised
register?

> +void npcm_dwmac_pcs_init(struct npcm_dwmac *dwmac, struct device *dev,
> +			 struct plat_stmmacenet_data *plat_dat)
> +{
> +	u16 val;
> +
> +	iowrite16((u16)(SR_MII_CTRL >> 9), dwmac->reg + IND_AC_BA_REG);
> +	val = ioread16(dwmac->reg + PCS_SR_MII_CTRL_REG);
> +	val |= PCS_RST;
> +	iowrite16(val, dwmac->reg + PCS_SR_MII_CTRL_REG);
> +
> +	while (val & PCS_RST)
> +		val = ioread16(dwmac->reg + PCS_SR_MII_CTRL_REG);

What if the PCS never clears its reset bit? Maybe use
read_poll_timeout() ?

> +
> +	val &= ~(PCS_AN_ENABLE);
> +	iowrite16(val, dwmac->reg + PCS_SR_MII_CTRL_REG);
> +}

Also, maybe it's time to require new stmmac platform support to start
making use of the phylink PCS support rather than continuing to code its
own?

I notice, however, that you always disable inband signalling - please
explain why. Also, what protocol does the PCS use when communicating
with the PHY?

-- 
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