Re: [PATCH net-next 3/7] net: mscc: ocelot: optimize ocelot_mm_irq()

[Simon Horman <simon.horman@corigine.com>]

On Sat, Apr 15, 2023 at 08:05:47PM +0300, Vladimir Oltean wrote:
> The MAC Merge IRQ of all ports is shared with the PTP TX timestamp IRQ
> of all ports, which means that currently, when a PTP TX timestamp is
> generated, felix_irq_handler() also polls for the MAC Merge layer status
> of all ports, looking for changes. This makes the kernel do more work,
> and under certain circumstances may make ptp4l require a
> tx_timestamp_timeout argument higher than before.
> 
> Changes to the MAC Merge layer status are only to be expected under
> certain conditions - its TX direction needs to be enabled - so we can
> check early if that is the case, and omit register access otherwise.
> 
> Make ocelot_mm_update_port_status() skip register access if
> mm->tx_enabled is unset, and also call it once more, outside IRQ
> context, from ocelot_port_set_mm(), when mm->tx_enabled transitions from
> true to false, because an IRQ is also expected in that case.
> 
> Also, a port may have its MAC Merge layer enabled but it may not have
> generated the interrupt. In that case, there's no point in writing to
> DEV_MM_STATUS to acknowledge that IRQ. We can reduce the number of
> register writes per port with MM enabled by keeping an "ack" variable
> which writes the "write-one-to-clear" bits. Those are 3 in number:
> PRMPT_ACTIVE_STICKY, UNEXP_RX_PFRM_STICKY and UNEXP_TX_PFRM_STICKY.
> The other fields in DEV_MM_STATUS are read-only and it doesn't matter
> what is written to them, so writing zero is just fine.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Simon Horman <simon.horman@corigine.com>

No need to respin on my account.
However, I do observe that this patch is doing several things,
and I do wonder if it could have been more than one patch.