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SubjectRe: [PATCH net v3 1/1] net: pcs: xpcs: fix incorrect CL37 AN sequence
Date
On Fri, Oct 01, 2021 at 10:57:30AM +0100, Russell King (Oracle) wrote:
> On Fri, Oct 01, 2021 at 12:19:52AM +0000, Vladimir Oltean wrote:
> > static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs, unsigned int mode)
> > {
> > int ret, mdio_ctrl1, old_an_ctrl, an_ctrl, old_dig_ctrl1, dig_ctrl1;
> >
> > /* Disable SGMII AN in case it is already enabled */
> > mdio_ctrl1 = xpcs_read(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_CTRL);
> > if (mdio_ctrl1 < 0)
> > return mdio_ctrl1;
> >
> > if (mdio_ctrl1 & AN_CL37_EN) {
> > ret = xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_CTRL,
> > mdio_ctrl1 & ~AN_CL37_EN);
> > if (ret < 0)
> > return ret;
> > }
>
> This is fine...
>
> > if (!(mdio_ctrl1 & AN_CL37_EN) && phylink_autoneg_inband(mode)) {
> > ret = xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_CTRL,
> > mdio_ctrl1 | AN_CL37_EN);
> > if (ret)
> > return ret;
> > }
>
> This is not. If the control register had AN_CL37_EN set initially, then
> in the first test above, we clear the bit. However, mdio_ctrl1 will
> still contain the bit set. When we get here, we will skip setting the
> register bit back to one even if in-band mode was requested.
>
> As I said in a previous email, at this point there is no reason to check
> the previous state, because if it was set on entry, we will have cleared
> it, so the register state at this point has the bit clear no matter
> what. If we need to set it, then we /always/ need to write it here - it
> doesn't matter what the initial state was.

Correct, it should have been:

if (phylink_autoneg_inband(mode)) {
ret = xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_CTRL,
mdio_ctrl1 | AN_CL37_EN);
if (ret)
return ret;
}

For the record, just in case this code gets copied anywhere, there's
another mistake in my placement of one of the comments.

/* If using in-band autoneg, enable automatic speed/duplex mode change
* by HW after SGMII AN complete.
* 5) VR_MII_MMD_CTRL Bit(12) [AN_ENABLE] = 1b (Enable SGMII AN) <- this part of the comment
*/
old_dig_ctrl1 = xpcs_read(xpcs, MDIO_MMD_VEND2, DW_VR_MII_DIG_CTRL1);
if (old_dig_ctrl1 < 0)
return old_dig_ctrl1;

really belongs here:

/* If using SGMII AN, enable it here */
if (phylink_autoneg_inband(mode)) {
ret = xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_MMD_CTRL,
mdio_ctrl1 | AN_CL37_EN);
if (ret)
return ret;
}
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