[PATCH net] net: stmmac: dwmac-stm32: fix resume on STM32 MCU

[Ben Wolsieffer <ben.wolsieffer@hefring.com>]

The STM32MP1 keeps clk_rx enabled during suspend, and therefore the
driver does not enable the clock in stm32_dwmac_init() if the device was
suspended. The problem is that this same code runs on STM32 MCUs, which
do disable clk_rx during suspend, causing the clock to never be
re-enabled on resume.

This patch adds a variant flag to indicate that clk_rx remains enabled
during suspend, and uses this to decide whether to enable the clock in
stm32_dwmac_init() if the device was suspended.

This approach fixes this specific bug with limited opportunity for
unintended side-effects, but I have a follow up patch that will refactor
the clock configuration and hopefully make it less error prone.

Fixes: 6528e02cc9ff ("net: ethernet: stmmac: add adaptation for stm32mp157c.")
Signed-off-by: Ben Wolsieffer <ben.wolsieffer@hefring.com>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-stm32.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-stm32.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-stm32.c
index bdb4de59a672..28c8ca5fba6c 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-stm32.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-stm32.c
@@ -105,6 +105,7 @@ struct stm32_ops {
 	int (*parse_data)(struct stm32_dwmac *dwmac,
 			  struct device *dev);
 	u32 syscfg_eth_mask;
+	bool clk_rx_enable_in_suspend;
 };
 
 static int stm32_dwmac_init(struct plat_stmmacenet_data *plat_dat)
@@ -122,7 +123,8 @@ static int stm32_dwmac_init(struct plat_stmmacenet_data *plat_dat)
 	if (ret)
 		return ret;
 
-	if (!dwmac->dev->power.is_suspended) {
+	if (!dwmac->ops->clk_rx_enable_in_suspend ||
+	    !dwmac->dev->power.is_suspended) {
 		ret = clk_prepare_enable(dwmac->clk_rx);
 		if (ret) {
 			clk_disable_unprepare(dwmac->clk_tx);
@@ -514,7 +516,8 @@ static struct stm32_ops stm32mp1_dwmac_data = {
 	.suspend = stm32mp1_suspend,
 	.resume = stm32mp1_resume,
 	.parse_data = stm32mp1_parse_data,
-	.syscfg_eth_mask = SYSCFG_MP1_ETH_MASK
+	.syscfg_eth_mask = SYSCFG_MP1_ETH_MASK,
+	.clk_rx_enable_in_suspend = true
 };
 
 static const struct of_device_id stm32_dwmac_match[] = {
-- 
2.42.0