[PATCH net-next v16 1/7] net: stmmac: dwmac4: don't program the 1us tick counter without a CSR clock

[Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>]

dwmac4_core_init() derives the TIC counter value from the rate of the CSR
clock. If no such clock is available (for instance because clocks are
managed by firmware and not described in DT), the rate is 0 and
(0 / 1000000) - 1 underflows to 0xffffffff, which is then written
to the register and can break the LPI timers that count in microseconds.

Leave the register at its reset value when the CSR clock rate is
unknown. The RX watchdog conversion helpers already cope with a missing
clock by falling back to clk_ref_rate or returning 0, so nothing else
needs to change.

This is first hit with the Qualcomm sa8255p ethernet, whose DT has no
clocks.

Fixes: 68f5d3dc2808 ("net: stmmac: qcom-ethqos: add support for sa8255p")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/179052656185.2160803.1751830002645522416@kernel.org/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
index cd6c5d6f42b5445918f277a2b4168d8f473bfca1..259e2ebed8c14dfdb9318da9be03c5f1dc9b1284 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c
@@ -48,9 +48,14 @@ static void dwmac4_core_init(struct mac_device_info *hw,
 	value = readl(ioaddr + GMAC_CONFIG);
 	writel(value | GMAC_CORE_INIT, ioaddr + GMAC_CONFIG);
 
-	/* Configure LPI 1us counter to number of CSR clock ticks in 1us - 1 */
+	/* Configure LPI 1us counter to number of CSR clock ticks in 1us - 1.
+	 * Platforms with firmware-managed clocks may not expose the CSR clock
+	 * to linux, in which case there's no meaningful value to program.
+	 */
 	clk_rate = clk_get_rate(priv->plat->stmmac_clk);
-	writel((clk_rate / 1000000) - 1, ioaddr + GMAC4_MAC_ONEUS_TIC_COUNTER);
+	if (clk_rate >= 1000000)
+		writel((clk_rate / 1000000) - 1,
+		       ioaddr + GMAC4_MAC_ONEUS_TIC_COUNTER);
 
 	/* Enable GMAC interrupts */
 	writel(GMAC_INT_DEFAULT_ENABLE, ioaddr + GMAC_INT_EN);

-- 
2.47.3


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