Subject: Re: [net-next PATCH v3 3/3] net: phy: Add Airoha AN8855 Internal Switch Gigabit PHY

From: Christian Marangi <[email-masked]>
Date: Fri, 8 Nov 2024 14:09:22 +0100

On Fri, Nov 08, 2024 at 11:09:30AM +0000, Russell King (Oracle) wrote:
> On Wed, Nov 06, 2024 at 01:22:38PM +0100, Christian Marangi wrote:
> > +/* MII Registers Page 1 */
> > +#define AN8855_PHY_EXT_REG_14			0x14
> > +#define   AN8855_PHY_EN_DOWN_SHFIT		BIT(4)
> 
> Shouldn't "AN8855_PHY_EN_DOWN_SHFIT" be "AN8855_PHY_EN_DOWN_SHIFT"
> (notice the I and F are swapped) ?
>

Typo from SDK that I didn't notice fun.

> > +static int an8855_get_downshift(struct phy_device *phydev, u8 *data)
> > +{
> > +	int saved_page;
> > +	int val;
> > +	int ret;
> > +
> > +	saved_page = phy_select_page(phydev, AN8855_PHY_PAGE_EXTENDED_1);
> > +	if (saved_page >= 0)
> > +		val = __phy_read(phydev, AN8855_PHY_EXT_REG_14);
> > +	ret = phy_restore_page(phydev, saved_page, val);
> > +	if (ret)
> > +		return ret;
> 
> This function is entirely broken.
> 
> phy_restore_page() will return "val" if everything went successfully,
> so here you end up returning "val" via this very return statement
> without executing any further code in the function. The only time
> further code will be executed is if "val" was successfully read as
> zero.
> 
> Please use the helpers provided:
> 
> 	ret = phy_read_paged(phydev, AN8855_PHY_PAGE_EXTENDED_1,
> 			     AN8855_PHY_EXT_REG_14);
> 	if (ret < 0)
> 		return ret;
> 
> ret now contains what you're using as "val" below. No need to open code
> phy_read_paged().

Thanks for the explaination, totally got confused by reading the
restore_page code. Anyway yes I will use the helper.

> 
> > +
> > +	*data = val & AN8855_PHY_EXT_REG_14 ? DOWNSHIFT_DEV_DEFAULT_COUNT :
> > +					      DOWNSHIFT_DEV_DISABLE;
> 
> Here, the test is against the register number rather than the bit that
> controls downshift. Shouldn't AN8855_PHY_EXT_REG_14 be
> AN8855_PHY_EN_DOWN_SH(F)I(F)T ?

Copy paste error, was already staged to fix, thanks for extra eye on
this.

> 
> > +static int an8855_set_downshift(struct phy_device *phydev, u8 cnt)
> > +{
> > +	int saved_page;
> > +	int ret;
> > +
> > +	saved_page = phy_select_page(phydev, AN8855_PHY_PAGE_EXTENDED_1);
> > +	if (saved_page >= 0) {
> > +		if (cnt != DOWNSHIFT_DEV_DISABLE)
> > +			ret = __phy_set_bits(phydev, AN8855_PHY_EXT_REG_14,
> > +					     AN8855_PHY_EN_DOWN_SHFIT);
> > +		else
> > +			ret = __phy_clear_bits(phydev, AN8855_PHY_EXT_REG_14,
> > +					       AN8855_PHY_EN_DOWN_SHFIT);
> > +	}
> > +
> > +	return phy_restore_page(phydev, saved_page, ret);
> 
> This entire thing can be simplified to:
> 
> 	u16 ds = cnt != DOWNSHIFT_DEV_DISABLE ? AN8855_PHY_EN_DOWN_SHFIT: 0;
> 
> 	return phy_modify_paged(phydev, AN8855_PHY_PAGE_EXTENDED_1,
> 				AN8855_PHY_EXT_REG_14, AN8855_PHY_EN_DOWN_SHFIT,
> 				ds);

Funnly in rechecking I produced the same exact change.

> Thanks.

Thanks to you for the review.

> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

-- 
	Ansuel