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

Fri Aug 26 13:36:46 PDT 2022

On 26.08.2022 17:45, Da Xue wrote:
> Hi Heiner,
> 
> I have been running with the patch reverted for about two weeks now
> without issue but I have a modified u-boot with ethernet bringup
> disabled.
> 
> If u-boot brings up ethernet, all of the GXL boards with more than 1GB
> memory experience various bugs. I had to bring the PHY initialization
> patch into Linux proper:
> https://github.com/libre-computer-project/libretech-linux/commit/1a4004c11877d4239b57b182da1ce69a81c0150c
> 
Thanks for the follow-up. To be acceptable upstream I'm pretty sure that
the maintainer is going to request replacing magic number 0x10110181
with or'ing proper constants for the respective bits and fields.

> Hope this helps someone.
> 
> Best,
> 
> Da
> 
> On Fri, Aug 26, 2022 at 5:51 AM Heiner Kallweit <hkallweit1 at gmail.com> wrote:
>>
>> 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.