netdev - Re: [PATCH v3 net-next 3/5] dsa: add DSA switch driver for Microchip KSZ9477

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Date:   Mon, 22 May 2017 23:27:57 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Woojung.Huh@...rochip.com
Cc:     f.fainelli@...il.com, vivien.didelot@...oirfairelinux.com,
        sergei.shtylyov@...entembedded.com, netdev@...r.kernel.org,
        davem@...emloft.net, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH v3 net-next 3/5] dsa: add DSA switch driver for Microchip
 KSZ9477

On Mon, May 22, 2017 at 09:21:28PM +0000, Woojung.Huh@...rochip.com wrote:
> Hi Andres,
> 
> > > +static struct {
> > > +	int index;
> > > +	char string[ETH_GSTRING_LEN];
> > 
> > Hi Woojung
> > 
> > Since you need to respin for the skb_put_padto(), please make this
> > const.
> OK.
> 
> > > +static int get_vlan_table(struct dsa_switch *ds, u16 vid, u32 *vlan_table)
> > > +{
> > > +	struct ksz_device *dev = ds->priv;
> > > +	u8 data;
> > > +	int timeout = 1000;
> > > +
> > > +	ksz_write16(dev, REG_SW_VLAN_ENTRY_INDEX__2, vid &
> > VLAN_INDEX_M);
> > > +	ksz_write8(dev, REG_SW_VLAN_CTRL, VLAN_READ | VLAN_START);
> > > +
> > > +	/* wait to be cleared */
> > > +	data = 0;
> > > +	do {
> > > +		ksz_read8(dev, REG_SW_VLAN_CTRL, &data);
> > > +		if (!(data & VLAN_START))
> > > +			break;
> > > +		usleep_range(1, 10);
> > > +	} while (timeout-- > 0);
> > > +
> > > +	if (!timeout)
> > > +		return -ETIMEDOUT;
> > > +
> > > +	ksz_read32(dev, REG_SW_VLAN_ENTRY__4, &vlan_table[0]);
> > > +	ksz_read32(dev, REG_SW_VLAN_ENTRY_UNTAG__4,
> > &vlan_table[1]);
> > > +	ksz_read32(dev, REG_SW_VLAN_ENTRY_PORTS__4, &vlan_table[2]);
> > > +
> > > +	ksz_write8(dev, REG_SW_VLAN_CTRL, 0);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static int set_vlan_table(struct dsa_switch *ds, u16 vid, u32 *vlan_table)
> > > +{
> > > +	struct ksz_device *dev = ds->priv;
> > > +	u8 data;
> > > +	int timeout = 1000;
> > > +
> > > +	ksz_write32(dev, REG_SW_VLAN_ENTRY__4, vlan_table[0]);
> > > +	ksz_write32(dev, REG_SW_VLAN_ENTRY_UNTAG__4, vlan_table[1]);
> > > +	ksz_write32(dev, REG_SW_VLAN_ENTRY_PORTS__4, vlan_table[2]);
> > > +
> > > +	ksz_write16(dev, REG_SW_VLAN_ENTRY_INDEX__2, vid &
> > VLAN_INDEX_M);
> > > +	ksz_write8(dev, REG_SW_VLAN_CTRL, VLAN_START | VLAN_WRITE);
> > > +
> > > +	do {
> > > +		ksz_read8(dev, REG_SW_VLAN_CTRL, &data);
> > > +		if (!(data & VLAN_START))
> > > +			break;
> > > +		usleep_range(1, 10);
> > > +	} while (timeout-- > 0);
> > > +
> > > +	if (!timeout)
> > > +		return -ETIMEDOUT;
> > > +
> > > +	ksz_write8(dev, REG_SW_VLAN_CTRL, 0);
> > > +
> > > +	mutex_lock(&dev->vlancache_mutex);
> > 
> > Humm. I think this is wrong. Shouldn't you hold the mutex while you
> > change the hardware as well as the cache. Otherwise there is a risk
> > your cache could be different to the hardware when you get a race
> > between two threads?
> Thanks for pointing this out.
> Rather than two separate mutex (H/W and vlancache), will put one HW access mutex
> around get_vlan_table and set_vlan_table to cover vlancache access too. Even though
> little bit overhead. How do you think?

I would move the mutex_lock(&dev->vlancache_mutex) to be beginning of
the function. It then protects both the hardware and the vlan cache,
and keeps them synchronised.

    Andrew