Subject: Re: [PATCH v2 net] net: phy: mscc: Add error check when __phy_read() failed

From: "Russell King (Oracle)" <[email-masked]>
Date: Wed, 11 May 2022 11:45:24 +0100

On Tue, May 10, 2022 at 10:22:45PM +0800, Wan Jiabing wrote:
> Calling __phy_read() might return a negative error code. Use 'int'
> to declare variables which call __phy_read() and also add error check
> for them.
> 
> The numerous callers of vsc8584_macsec_phy_read() don't expect it to
> fail. So don't return the error code from __phy_read(), but also don't
> return random values if it does fail.
> 
> Fixes: fa164e40c53b ("net: phy: mscc: split the driver into separate files")
> Signed-off-by: Wan Jiabing <[email-masked]>
> ---
> Changelog:
> v2:
> - Sort variable declaration and add a detailed comment.
> ---
>  drivers/net/phy/mscc/mscc_macsec.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/phy/mscc/mscc_macsec.c b/drivers/net/phy/mscc/mscc_macsec.c
> index b7b2521c73fb..58ad11a697b6 100644
> --- a/drivers/net/phy/mscc/mscc_macsec.c
> +++ b/drivers/net/phy/mscc/mscc_macsec.c
> @@ -22,9 +22,9 @@
>  static u32 vsc8584_macsec_phy_read(struct phy_device *phydev,
>  				   enum macsec_bank bank, u32 reg)
>  {
> -	u32 val, val_l = 0, val_h = 0;
> +	int rc, val, val_l, val_h;
>  	unsigned long deadline;
> -	int rc;
> +	u32 ret = 0;
>  
>  	rc = phy_select_page(phydev, MSCC_PHY_PAGE_MACSEC);
>  	if (rc < 0)
> @@ -47,15 +47,20 @@ static u32 vsc8584_macsec_phy_read(struct phy_device *phydev,
>  	deadline = jiffies + msecs_to_jiffies(PROC_CMD_NCOMPLETED_TIMEOUT_MS);
>  	do {
>  		val = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_19);
> +		if (val < 0)
> +			goto failed;
>  	} while (time_before(jiffies, deadline) && !(val & MSCC_PHY_MACSEC_19_CMD));
>  
>  	val_l = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_17);
>  	val_h = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_18);
>  
> +	if (val_l > 0 && val_h > 0)
> +		ret = (val_h << 16) | val_l;
> +
>  failed:
>  	phy_restore_page(phydev, rc, rc);
>  
> -	return (val_h << 16) | val_l;
> +	return ret;
>  }

This is still wrong - phy_restore_page() can fail to retore the page.

It's rather unfortunate that you need to return a u32, where the
high values become negative ints, which means you can't use
phy_restore_page() as it's supposed to be used.

If you fail to read from the PHY, is returning zero acceptable?

I think what you should be doing at the very least is:

	rc = phy_select_page(phydev, MSCC_PHY_PAGE_MACSEC);
	if (rc < 0)
		goto failed;

	rc = __phy_write(phydev, MSCC_EXT_PAGE_MACSEC_20, ...);
	if (rc < 0)
		goto failed;

	...

	rc = __phy_write(phydev, MSCC_EXT_PAGE_MACSEC_19, ...);
	if (rc < 0)
		goto failed;

	...
	do {
		val = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_19);
		if (val < 0) {
			rc = val;
			goto failed;
		}
	} while (...);

	val_l = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_17);
	if (val_l < 0) {
		rc = val_l;
		goto failed;
	}

	val_h = __phy_read(phydev, MSCC_EXT_PAGE_MACSEC_18);
	if (val_h < 0)
		rc = val_h;

failed:
	rc = phy_restore_page(phgydev, rc, 0);

	return rc < 0 ? 0 : val_h << 16 | val_l;

Which means that if any of the PHY IO functions fail at any point, this
returns zero.

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