[PATCH] net: stmmac: Initialize MAC_ONEUS_TIC_COUNTER register

[Harald Seiler]

Hi Marek,

On Sun, 2023-05-07 at 01:58 +0200, Marek Vasut wrote:
> Initialize MAC_ONEUS_TIC_COUNTER register with correct value derived
> from CSR clock, otherwise EEE is unstable on at least NXP i.MX8M Plus
> and Micrel KSZ9131RNX PHY, to the point where not even ARP request can
> be sent out.
> 
> i.MX 8M Plus Applications Processor Reference Manual, Rev. 1, 06/2021
> 11.7.6.1.34 One-microsecond Reference Timer (MAC_ONEUS_TIC_COUNTER)
> defines this register as:
> "
> This register controls the generation of the Reference time (1 microsecond
> tic) for all the LPI timers. This timer has to be programmed by the software
> initially.
> ...
> The application must program this counter so that the number of clock cycles
> of CSR clock is 1us. (Subtract 1 from the value before programming).
> For example if the CSR clock is 100MHz then this field needs to be programmed
> to value 100 - 1 = 99 (which is 0x63).
> This is required to generate the 1US events that are used to update some of
> the EEE related counters.
> "
> 
> The reset value is 0x63 on i.MX8M Plus, which means expected CSR clock are
> 100 MHz. However, the i.MX8M Plus "enet_qos_root_clk" are 266 MHz instead,
> which means the LPI timers reach their count much sooner on this platform.
> 
> This is visible using a scope by monitoring e.g. exit from LPI mode on TX_CTL
> line from MAC to PHY. This should take 30us per STMMAC_DEFAULT_TWT_LS setting,
> during which the TX_CTL line transitions from tristate to low, and 30 us later
> from low to high. On i.MX8M Plus, this transition takes 11 us, which matches
> the 30us * 100/266 formula for misconfigured MAC_ONEUS_TIC_COUNTER register.
> 
> Configure MAC_ONEUS_TIC_COUNTER based on CSR clock, so that the LPI timers
> have correct 1us reference. This then fixes EEE on i.MX8M Plus with Micrel
> KSZ9131RNX PHY.
> 
> Signed-off-by: Marek Vasut <marex at denx.de>

Tested on STM32MP157 with KSZ9131RNX at 1000Mb/s.  This patch makes the
network as reliable with EEE active as it is with EEE disabled.  So

Tested-by: Harald Seiler <hws at denx.de>

> ---
> NOTE: The hint that this might be related to LPI timer misconfiguration
>       came from sending large fragmented ICMP request, i.e.
>       ping -4 -c 1 -s 4096 -I eth1 192.168.1.1
>       The received packets consistently missed the 1st fragment, because
>       the LPI exit time was too short and the first packet was likely
>       pushed out of the MAC while the PHY was still not ready for it.
> NOTE: I suspect this can help with Toradex ELB-3757, Marcel, can you please
>       test this patch on i.MX8M Plus Verdin ?
>       https://developer-archives.toradex.com/software/linux/release-details?module=Verdin+iMX8M+Plus&key=ELB-3757
> NOTE: STM32MP15xx sets 'ethmac' clock to 266.5 MHz, so this patch likely
>       helps there as well. The default value of MAC_ONEUS_TIC_COUNTER on
>       this platform is also 0x63, i.e. expected 100 MHz CSR clock. I can
>       not test this with KSZ9131RNX as I do not have any STM32MP15xx
>       board with this PHY. Harald, can you please test ?
> ---
> Cc: "David S. Miller" <davem at davemloft.net>
> Cc: Alexandre Torgue <alexandre.torgue at foss.st.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Cc: Francesco Dolcini <francesco.dolcini at toradex.com>
> Cc: Giuseppe Cavallaro <peppe.cavallaro at st.com>
> Cc: Harald Seiler <hws at denx.de>
> Cc: Jakub Kicinski <kuba at kernel.org>
> Cc: Jose Abreu <joabreu at synopsys.com>
> Cc: Marcel Ziswiler <marcel.ziswiler at toradex.com>
> Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
> Cc: Paolo Abeni <pabeni at redhat.com>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-stm32 at st-md-mailman.stormreply.com
> Cc: netdev at vger.kernel.org
> ---
>  drivers/net/ethernet/stmicro/stmmac/dwmac4.h      | 1 +
>  drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> index 4538f334df576..d3c5306f1c41f 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4.h
> @@ -181,6 +181,7 @@ enum power_event {
>  #define GMAC4_LPI_CTRL_STATUS	0xd0
>  #define GMAC4_LPI_TIMER_CTRL	0xd4
>  #define GMAC4_LPI_ENTRY_TIMER	0xd8
> +#define GMAC4_MAC_ONEUS_TIC_COUNTER	0xdc
>  
>  /* LPI control and status defines */
>  #define GMAC4_LPI_CTRL_STATUS_LPITCSE	BIT(21)	/* LPI Tx Clock Stop Enable */
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> index afaec3fb9ab66..03b1c5a97826e 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
> @@ -25,6 +25,7 @@ static void dwmac4_core_init(struct mac_device_info *hw,
>  	struct stmmac_priv *priv = netdev_priv(dev);
>  	void __iomem *ioaddr = hw->pcsr;
>  	u32 value = readl(ioaddr + GMAC_CONFIG);
> +	u32 clk_rate;
>  
>  	value |= GMAC_CORE_INIT;
>  
> @@ -47,6 +48,10 @@ static void dwmac4_core_init(struct mac_device_info *hw,
>  
>  	writel(value, ioaddr + GMAC_CONFIG);
>  
> +	/* Configure LPI 1us counter to number of CSR clock ticks in 1us - 1 */
> +	clk_rate = clk_get_rate(priv->plat->stmmac_clk);
> +	writel((clk_rate / 1000000) - 1, ioaddr + GMAC4_MAC_ONEUS_TIC_COUNTER);
> +
>  	/* Enable GMAC interrupts */
>  	value = GMAC_INT_DEFAULT_ENABLE;
>