Messages in this thread | | | Date | Thu, 7 Dec 2023 19:48:29 +0200 | From | Vladimir Oltean <> | Subject | Re: [PATCH net-next 01/15] net: dsa: mt7530: always trap frames to active CPU port on MT7530 |
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On Sat, Dec 02, 2023 at 11:29:18AM +0300, Arınç ÜNAL wrote: > > I would be tempted to write this as: > > > > mask = BIT(cpu_dp->index); > > > > if (operational) > > priv->active_cpu_ports |= mask; > > else > > priv->active_cpu_ports &= ~mask; > > > > Now, what happens when active_cpu_ports is zero? Doesn't that mean there > > is no active CPU port? In which case, wouldn't disabling the CPU port > > direction be appropriate, such as: > > > > if (priv->active_cpu_ports) > > val = CPU_EN | CPU_PORT(__ffs(priv->active_cpu_ports)); > > else > > val = 0; > > > > mt7530_rmw(priv, MT7530_MFC, CPU_EN | CPU_PORT_MASK, val); > > > > ? > > In practice, it doesn't seem to matter. The CPU_EN bit enables the CPU port > defined on CPU_PORT_MASK which is used for trapping frames. No active CPU > ports would mean that all the DSA conduits are down. In that case, all the > user ports will be down also. So there won't be any traffic. But disabling > it is of course more appropriate here.
Ack, DSA takes down the user ports which are affine to a certain conduit interface when that goes down. See the NETDEV_GOING_DOWN handling in net/dsa/user.c.
> > > > > struct mt7530_priv { > > > struct device *dev; > > > @@ -786,6 +787,7 @@ struct mt7530_priv { > > > struct irq_domain *irq_domain; > > > u32 irq_enable; > > > int (*create_sgmii)(struct mt7530_priv *priv, bool dual_sgmii); > > > + unsigned long active_cpu_ports; > > > > So this will be 32 or 64 bit in size. Presumably you know how many CPU > > ports there can be, which looking at this code must be less than 8 as > > CPU_PORT_MASK is only 3 bits in size. So, maybe use a u8, and check > > that cpu_dp->index <= 7 ?
We picked "unsigned long" as storage because that's also the size of the argument that __ffs() takes. But admittedly, we could have also stored a smaller variable and promote it to unsigned long when we pass it to __ffs().
> Aren't there other mechanisms to check that cpu_dp->index is a valid port?
cpu_dp->index is guaranteed by DSA to be valid (according to the "reg" value from the device tree and smaller than ds->num_ports). It's just a question of balancing this kind of optimization with the possibility that a future switch appears which has more than MT7530_NUM_PORTS (7) ports.
> At least with phylink_get_caps(), only ports lower than 7 will have proper > interface modes allowed. > > Here's the code after you and Vladimir's review: > > static void > mt753x_conduit_state_change(struct dsa_switch *ds, > const struct net_device *conduit, > bool operational) > { > struct dsa_port *cpu_dp = conduit->dsa_ptr; > struct mt7530_priv *priv = ds->priv; > u8 mask; > int val; > > /* Set the CPU port to trap frames to for MT7530. Trapped frames will be > * forwarded to the numerically smallest CPU port which the DSA conduit > * interface its affine to is up. > */ > if (priv->id != ID_MT7530 && priv->id != ID_MT7621) > return; > > mask = BIT(cpu_dp->index); > > if (operational) > priv->active_cpu_ports |= mask; > else > priv->active_cpu_ports &= ~mask; > > if (priv->active_cpu_ports) > val = CPU_EN | CPU_PORT(__ffs(priv->active_cpu_ports)); > else > val = 0;
You could initialize "val" with 0 at declaration time and you wouldn't need the "else" branch.
> > mt7530_rmw(priv, MT7530_MFC, CPU_EN | CPU_PORT_MASK, val); > } > > struct mt7530_priv { > [...] > u8 active_cpu_ports; > };
Actually, looking at the code now, I don't understand why we even keep track of the active_cpu_ports mask in the driver. We could read the MT7530_MFC register in mt753x_conduit_state_change(), flip the bit corresponding just to cpu_dp->index (rather than rmw all of CPU_PORT_MASK), and write back the result. And to address Russell's concern, we could test whether the resulting CPU_PORT_MASK portion of what we're going to write back is all-zeroes or not, and if it is, clear the CPU_EN bit, otherwise set it.
> > > > > I would also suggest moving irq_enable after create_sgmii, to avoid > > holes in the struct. > > Sorry, I've got no idea about this. Could you explain why would there > possibly be holes in the struct with the current ordering of the members of > the mt7530_priv structure? > > Arınç
FWIW:
$ pahole -C mt7530_priv $KBUILD_OUTPUT/drivers/net/dsa/mt7530.o struct mt7530_priv { struct device * dev; /* 0 8 */ struct dsa_switch * ds; /* 8 8 */ struct mii_bus * bus; /* 16 8 */ struct regmap * regmap; /* 24 8 */ struct reset_control * rstc; /* 32 8 */ struct regulator * core_pwr; /* 40 8 */ struct regulator * io_pwr; /* 48 8 */ struct gpio_desc * reset; /* 56 8 */ /* --- cacheline 1 boundary (64 bytes) --- */ const struct mt753x_info * info; /* 64 8 */ unsigned int id; /* 72 4 */ bool mcm; /* 76 1 */
/* XXX 3 bytes hole, try to pack */
phy_interface_t p6_interface; /* 80 4 */ phy_interface_t p5_interface; /* 84 4 */ unsigned int p5_intf_sel; /* 88 4 */ u8 mirror_rx; /* 92 1 */ u8 mirror_tx; /* 93 1 */
/* XXX 2 bytes hole, try to pack */
struct mt7530_port ports[7]; /* 96 168 */ /* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */ struct mt753x_pcs pcs[7]; /* 264 280 */ /* --- cacheline 8 boundary (512 bytes) was 32 bytes ago --- */ struct mutex reg_mutex; /* 544 32 */ /* --- cacheline 9 boundary (576 bytes) --- */ int irq; /* 576 4 */
/* XXX 4 bytes hole, try to pack */
struct irq_domain * irq_domain; /* 584 8 */ u32 irq_enable; /* 592 4 */
/* XXX 4 bytes hole, try to pack */
int (*create_sgmii)(struct mt7530_priv *, bool); /* 600 8 */ unsigned long active_cpu_ports; /* 608 8 */
/* size: 616, cachelines: 10, members: 24 */ /* sum members: 603, holes: 4, sum holes: 13 */ /* last cacheline: 40 bytes */ };
It's not like this makes any practical difference, as struct mt7530_priv isn't used from hot paths, but tidying it up is a good sign of clean, careful development, and of understanding memory alignment.
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