Re: [PATCH net-next v2 3/3] net: eth: fbnic: Add pma read and write access

[Paolo Abeni]

On 4/30/26 5:08 PM, mike.marciniszyn@xxxxxxxxx wrote:
> From: "Mike Marciniszyn (Meta)" <mike.marciniszyn@xxxxxxxxx>
> 
> Document the MDIO interface topology with an ASCII diagram
> showing the MAC, PCS (MMD 3), FEC, Separated PMA (MMD 8), and PMD
> (MMD 1) blocks and their interconnects. The diagram illustrates how
> 4 lanes connect the MAC through PCS, FEC, and PMA, then narrow to
> 2 lanes at the PMD.
> 
> The c45 read and write routines are enhanced to support
> read and write of the separated PMA for the fbnic.
> 
> Co-developed-by: Alexander Duyck <alexanderduyck@xxxxxx>
> Signed-off-by: Alexander Duyck <alexanderduyck@xxxxxx>
> Signed-off-by: Mike Marciniszyn (Meta) <mike.marciniszyn@xxxxxxxxx>
> ---
> v2:
>   - no changes
> v1: https://lore.kernel.org/all/20260428172810.175077-5-mike.marciniszyn@xxxxxxxxx/
> 
>  drivers/net/ethernet/meta/fbnic/fbnic_csr.h  |  1 +
>  drivers/net/ethernet/meta/fbnic/fbnic_mdio.c | 71 ++++++++++++++++++++
>  2 files changed, 72 insertions(+)
> 
> diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_csr.h b/drivers/net/ethernet/meta/fbnic/fbnic_csr.h
> index 81794bd326e1..64b958df7774 100644
> --- a/drivers/net/ethernet/meta/fbnic/fbnic_csr.h
> +++ b/drivers/net/ethernet/meta/fbnic/fbnic_csr.h
> @@ -805,6 +805,7 @@ enum {
>  #define FBNIC_CSR_END_PCS		0x10668 /* CSR section delimiter */
> 
>  #define FBNIC_CSR_START_RSFEC		0x10800 /* CSR section delimiter */
> +#define FBNIC_RSFEC_CONTROL(n)	(0x10800 + 8 * (n))	/* 0x42000 + 32*n */

Sashiko says:

---
With the introduction of the RSFEC memory space at 0x10800, does the bounds
check in fbnic_mdio_write_pcs() need to be updated to prevent clobbering
these new registers?
While not introduced by this patch, fbnic_mdio_write_pcs() currently
contains:
    /* Allow access to both halves of PCS for 50R2 config */
    if (addr > 2)
        return;
When addr is 2, FBNIC_PCS_PAGE(2) evaluates to 0x10000 + 0x400 * 2, which
is 0x10800.
Since this overlaps with FBNIC_CSR_START_RSFEC, an MDIO write to MMD 3
(PCS) at address 2 could silently overwrite the newly managed RSFEC
control registers.
The read function fbnic_mdio_read_pcs() correctly uses if (addr >= 2) to
prevent this. Should the write function be updated to match?
---

Does not look blocking to me, but a follow-up could be needed.

/P