Subject: Re: [RFC 03/11] net: phy: refactor c45 phy identification sequence

From: Russell King - ARM Linux admin <[email-masked]>
Date: Sat, 23 May 2020 19:30:58 +0100

On Fri, May 22, 2020 at 04:30:51PM -0500, Jeremy Linton wrote:
> Lets factor out the phy id logic, and make it generic
> so that it can be used for c22 and c45.
> 
> Signed-off-by: Jeremy Linton <[email-masked]>
> ---
>  drivers/net/phy/phy_device.c | 65 +++++++++++++++++++-----------------
>  1 file changed, 35 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 7746c07b97fe..f0761fa5e40b 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -695,6 +695,29 @@ static int get_phy_c45_devs_in_pkg(struct mii_bus *bus, int addr, int dev_addr,
>  	return 0;
>  }
>  
> +static int _get_phy_id(struct mii_bus *bus, int addr, int dev_addr,
> +		       u32 *phy_id, bool c45)
> +{
> +	int phy_reg, reg_addr;
> +
> +	int reg_base = c45 ? (MII_ADDR_C45 | dev_addr << 16) : 0;

	int phy_reg, reg_addr, reg_base;

	reg_base = c45 ? (MII_ADDR_C45 | dev_addr << 16) : 0;

I think would be preferable.

> +
> +	reg_addr =  reg_base | MII_PHYSID1;
> +	phy_reg = mdiobus_read(bus, addr, reg_addr);
> +	if (phy_reg < 0)
> +		return -EIO;
> +
> +	*phy_id = phy_reg << 16;
> +
> +	reg_addr = reg_base | MII_PHYSID2;
> +	phy_reg = mdiobus_read(bus, addr, reg_addr);
> +	if (phy_reg < 0)
> +		return -EIO;
> +	*phy_id |= phy_reg;

The line spacing seems to be a little inconsistent between the above two
register reads.

> +
> +	return 0;
> +}

So, _get_phy_id() returns either zero or -EIO.

> +
>  static bool valid_phy_id(int val)
>  {
>  	return (val > 0 && ((val & 0x1fffffff) != 0x1fffffff));
> @@ -715,17 +738,17 @@ static bool valid_phy_id(int val)
>   */
>  static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>  			   struct phy_c45_device_ids *c45_ids) {
> -	int phy_reg;
> -	int i, reg_addr;
> +	int ret;
> +	int i;
>  	const int num_ids = ARRAY_SIZE(c45_ids->device_ids);
>  	u32 *devs = &c45_ids->devices_in_package;

I feel a "reverse christmas tree" complaint brewing... yes, the original
code didn't follow it.  Maybe a tidy up while touching this code?

>  
>  	/* Find first non-zero Devices In package. Device zero is reserved
>  	 * for 802.3 c45 complied PHYs, so don't probe it at first.
>  	 */
> -	for (i = 1; i < num_ids && *devs == 0; i++) {
> -		phy_reg = get_phy_c45_devs_in_pkg(bus, addr, i, devs);
> -		if (phy_reg < 0)
> +	for (i = 0; i < num_ids && *devs == 0; i++) {
> +		ret = get_phy_c45_devs_in_pkg(bus, addr, i, devs);
> +		if (ret < 0)
>  			return -EIO;
>  
>  		if ((*devs & 0x1fffffff) == 0x1fffffff) {
> @@ -752,17 +775,9 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>  		if (!(c45_ids->devices_in_package & (1 << i)))
>  			continue;
>  
> -		reg_addr = MII_ADDR_C45 | i << 16 | MII_PHYSID1;
> -		phy_reg = mdiobus_read(bus, addr, reg_addr);
> -		if (phy_reg < 0)
> -			return -EIO;
> -		c45_ids->device_ids[i] = phy_reg << 16;
> -
> -		reg_addr = MII_ADDR_C45 | i << 16 | MII_PHYSID2;
> -		phy_reg = mdiobus_read(bus, addr, reg_addr);
> -		if (phy_reg < 0)
> -			return -EIO;
> -		c45_ids->device_ids[i] |= phy_reg;
> +		ret = _get_phy_id(bus, addr, i, &c45_ids->device_ids[i], true);
> +		if (ret < 0)
> +			return ret;

So here we can only propagate the -EIO, so this keeps the semantics.

>  	}
>  	*phy_id = 0;
>  	return 0;
> @@ -787,27 +802,17 @@ static int get_phy_c45_ids(struct mii_bus *bus, int addr, u32 *phy_id,
>  static int get_phy_id(struct mii_bus *bus, int addr, u32 *phy_id,
>  		      bool is_c45, struct phy_c45_device_ids *c45_ids)
>  {
> -	int phy_reg;
> +	int ret;
>  
>  	if (is_c45)
>  		return get_phy_c45_ids(bus, addr, phy_id, c45_ids);
>  
> -	/* Grab the bits from PHYIR1, and put them in the upper half */
> -	phy_reg = mdiobus_read(bus, addr, MII_PHYSID1);
> -	if (phy_reg < 0) {
> +	ret = _get_phy_id(bus, addr, 0, phy_id, false);
> +	if (ret < 0) {
>  		/* returning -ENODEV doesn't stop bus scanning */
> -		return (phy_reg == -EIO || phy_reg == -ENODEV) ? -ENODEV : -EIO;
> +		return (ret == -EIO || ret == -ENODEV) ? -ENODEV : -EIO;

Since ret will only ever be -EIO here, this can only ever return
-ENODEV, which is a functional change in the code (probably unintended.)
Nevertheless, it's likely introducing a bug if the intention is for
some other return from mdiobus_read() to be handled differently.

>  	}
>  
> -	*phy_id = phy_reg << 16;
> -
> -	/* Grab the bits from PHYIR2, and put them in the lower half */
> -	phy_reg = mdiobus_read(bus, addr, MII_PHYSID2);
> -	if (phy_reg < 0)
> -		return -EIO;

... whereas this one always returns -EIO on any error.

So, I think you have the potential in this patch to introduce a subtle
change of behaviour, which may lead to problems - have you closely
analysed why the code was the way it was, and whether your change of
behaviour is actually valid?

> -
> -	*phy_id |= phy_reg;
> -
>  	return 0;
>  }
> -- 
> 2.26.2

-- 
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