[RFC/RFT PATCH] net: stmmac: do not poke MAC_CTRL_REG twice on link up

[Heiner Kallweit]

On 07.07.2022 12:14, Jerome Brunet wrote:
> For some reason, poking MAC_CTRL_REG a second time, even with the same
> value, causes problem on a dwmac 3.70a.
> 
> This problem happens on all the Amlogic SoCs, on link up, when the RMII
> 10/100 internal interface is used. The problem does not happen on boards
> using the external RGMII 10/100/1000 interface. Initially we suspected the
> PHY to be the problem but after a lot of testing, the problem seems to be
> coming from the MAC controller.
> 
>> meson8b-dwmac c9410000.ethernet: IRQ eth_wake_irq not found
>> meson8b-dwmac c9410000.ethernet: IRQ eth_lpi not found
>> meson8b-dwmac c9410000.ethernet: PTP uses main clock
>> meson8b-dwmac c9410000.ethernet: User ID: 0x11, Synopsys ID: 0x37
>> meson8b-dwmac c9410000.ethernet: 	DWMAC1000
>> meson8b-dwmac c9410000.ethernet: DMA HW capability register supported
>> meson8b-dwmac c9410000.ethernet: RX Checksum Offload Engine supported
>> meson8b-dwmac c9410000.ethernet: COE Type 2
>> meson8b-dwmac c9410000.ethernet: TX Checksum insertion supported
>> meson8b-dwmac c9410000.ethernet: Wake-Up On Lan supported
>> meson8b-dwmac c9410000.ethernet: Normal descriptors
>> meson8b-dwmac c9410000.ethernet: Ring mode enabled
>> meson8b-dwmac c9410000.ethernet: Enable RX Mitigation via HW Watchdog Timer
> 
> The problem is not systematic. Its occurence is very random from 1/50 to
> 1/2. It is fairly easy to detect by setting the kernel to boot over NFS and
> possibly setting it to reboot automatically when reaching the prompt.
> 
> When problem happens, the link is reported up by the PHY but no packet are
> actually going out. DHCP requests eventually times out and the kernel reset
> the interface. It may take several attempts but it will eventually work.
> 
>> meson8b-dwmac ff3f0000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
>> Sending DHCP requests ...... timed out!
>> meson8b-dwmac ff3f0000.ethernet eth0: Link is Down
>> IP-Config: Retrying forever (NFS root)...
>> meson8b-dwmac ff3f0000.ethernet eth0: PHY [0.1:08] driver [Meson G12A Internal PHY] (irq=POLL)
>> meson8b-dwmac ff3f0000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
>> meson8b-dwmac ff3f0000.ethernet eth0: No Safety Features support found
>> meson8b-dwmac ff3f0000.ethernet eth0: PTP not supported by HW
>> meson8b-dwmac ff3f0000.ethernet eth0: configuring for phy/rmii link mode
>> meson8b-dwmac ff3f0000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
>> Sending DHCP requests ...... timed out!
>> meson8b-dwmac ff3f0000.ethernet eth0: Link is Down
>> IP-Config: Retrying forever (NFS root)...
>> [...] 5 retries ...
>> IP-Config: Retrying forever (NFS root)...
>> meson8b-dwmac ff3f0000.ethernet eth0: PHY [0.1:08] driver [Meson G12A Internal PHY] (irq=POLL)
>> meson8b-dwmac ff3f0000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
>> meson8b-dwmac ff3f0000.ethernet eth0: No Safety Features support found
>> meson8b-dwmac ff3f0000.ethernet eth0: PTP not supported by HW
>> meson8b-dwmac ff3f0000.ethernet eth0: configuring for phy/rmii link mode
>> meson8b-dwmac ff3f0000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
>> Sending DHCP requests ., OK
>> IP-Config: Got DHCP answer from 10.1.1.1, my address is 10.1.3.229
> 
> Of course the same problem happens when not using NFS and it fairly
> difficult for IoT products to detect this situation and recover.
> 
> The call to stmmac_mac_set() should be no-op in our case, the bits it sets
> have already been set by an earlier call to stmmac_mac_set(). However
> removing this call solves the problem. We have no idea why or what is the
> actual problem.
> 
> Even weirder, keeping the call to stmmac_mac_set() but inserting a
> udelay(1) between writel() and stmmac_mac_set() solves the problem too.
> 
> Suggested-by: Qi Duan <qi.duan at amlogic.com>
> Signed-off-by: Jerome Brunet <jbrunet at baylibre.com>
> ---
> 
>  Hi,
> 
>  There is no intention to get this patch merged as it is.
>  It is sent with the hope to get a better understanding of the issue
>  and more testing.
> 
>  The discussion on this issue initially started on this thread
>  https://lore.kernel.org/all/CAK4VdL3-BEBzgVXTMejrAmDjOorvoGDBZ14UFrDrKxVEMD2Zjg@mail.gmail.com/
> 
>  The patches previously proposed in this thread have not solved the
>  problem.
> 
>  The line removed in this patch should be a no-op when it comes to the
>  value of MAC_CTRL_REG. So the change should make not a difference but
>  it does. Testing result have been very good so far so there must be an
>  unexpected consequence on the HW. I hope that someone with more
>  knowledge on this controller will be able to shine some light on this.
> 
>  Cheers
>  Jerome
> 
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index d1a7cf4567bc..3dca3cc61f39 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1072,7 +1072,6 @@ static void stmmac_mac_link_up(struct phylink_config *config,
>  
>  	writel(ctrl, priv->ioaddr + MAC_CTRL_REG);
>  
> -	stmmac_mac_set(priv, priv->ioaddr, true);
>  	if (phy && priv->dma_cap.eee) {
>  		priv->eee_active = phy_init_eee(phy, 1) >= 0;
>  		priv->eee_enabled = stmmac_eee_init(priv);

Now that we have a3a57bf07de2 ("net: stmmac: work around sporadic tx issue on link-up")
in linux-next and scheduled for stable:

Jerome, can you confirm that after this commit the following is no longer needed?
2c87c6f9fbdd ("net: phy: meson-gxl: improve link-up behavior")

Then I'd revert it, referencing the successor workaround / fix in stmmac.