[PATCH v2 2/2] net/nfp: write link speed to control BAR

[Chaoyong He]

> On 3/10/2023 6:25 AM, Chaoyong He wrote:
> > +	/**
> > +	 * Shift and mask nn_link_status so that it is effectively the value
> > +	 * at offset NFP_NET_CFG_STS_NSP_LINK_RATE.
> > +	 */
> > +	nn_link_status = (nn_link_status >>
> NFP_NET_CFG_STS_LINK_RATE_SHIFT) &
> > +			 NFP_NET_CFG_STS_LINK_RATE_MASK;
> 
> Thanks for extensive commenting, perhaps this is the source of confusion, I
> can't see how above logic makes effectively the value at offset LINK_RATE.
> 
> NFP_NET_CFG_STS_LINK_RATE_SHIFT = 1
> NFP_NET_CFG_STS_LINK_RATE_MASK  = 0xF
> 
> NFP_NET_CFG_STS               = 0x34
> NFP_NET_CFG_STS_NSP_LINK_RATE = 0x36
> 
> nfp_net_notify_port_speed()
> 	uint16_t speed;
> 	*(0x36) = speed
> 
> nfp_net_link_update()
> 	uint16_t val = *(0x34)
> 	val = (val >> 1) & 0xF;
> 
> 
> How come 'speed' and 'val' are same value?
> 
> Either there is a mistake or FW is making something in the background, I am
> trying to clarify this in past few comments but not able to yet.

Yes, here FW does do something in the background.
----------------------------------------------------------------------------

            16 bit write only                 16 bit read only

| x x x x x x x x x x x x y y y y | x x x x x x x x x x x y y y y x |

                                                 ^                                                ^

                                             0x36                                           0x34
------------------------------------------------------------------------------
The firmware confirm that whatever write into ‘yyyy’ field of 0x36 can be read from ‘yyyy’ field of 0x34.