[PATCH] net: mdio-ipq4019: add delay after clock enable

[PATCH] net: mdio-ipq4019: add delay after clock enable

[Baruch Siach]

From: Baruch Siach <baruch.siach@siklu.com>

Experimentation shows that PHY detect might fail when the code attempts
MDIO bus read immediately after clock enable. Add delay to stabilize the
clock before bus access.

PHY detect failure started to show after commit 7590fc6f80ac ("net:
mdio: Demote probed message to debug print") that removed coincidental
delay between clock enable and bus access.

10ms is meant to match the time it take to send the probed message over
UART at 115200 bps. This might be a far overshoot.

Fixes: 23a890d493e3 ("net: mdio: Add the reset function for IPQ MDIO driver")
Signed-off-by: Baruch Siach <baruch.siach@siklu.com>
---
 drivers/net/mdio/mdio-ipq4019.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mdio/mdio-ipq4019.c b/drivers/net/mdio/mdio-ipq4019.c
index 5f4cd24a0241..4eba5a91075c 100644
--- a/drivers/net/mdio/mdio-ipq4019.c
+++ b/drivers/net/mdio/mdio-ipq4019.c
@@ -200,7 +200,11 @@ static int ipq_mdio_reset(struct mii_bus *bus)
 	if (ret)
 		return ret;
 
-	return clk_prepare_enable(priv->mdio_clk);
+	ret = clk_prepare_enable(priv->mdio_clk);
+	if (ret == 0)
+		mdelay(10);
+
+	return ret;
 }
 
 static int ipq4019_mdio_probe(struct platform_device *pdev)
-- 
2.34.1

Re: [PATCH] net: mdio-ipq4019: add delay after clock enable

[Andrew Lunn]

On Mon, Feb 21, 2022 at 01:45:57PM +0200, Baruch Siach wrote:
> From: Baruch Siach <baruch.siach@siklu.com>
> 
> Experimentation shows that PHY detect might fail when the code attempts
> MDIO bus read immediately after clock enable. Add delay to stabilize the
> clock before bus access.
> 
> PHY detect failure started to show after commit 7590fc6f80ac ("net:
> mdio: Demote probed message to debug print") that removed coincidental
> delay between clock enable and bus access.
> 
> 10ms is meant to match the time it take to send the probed message over
> UART at 115200 bps. This might be a far overshoot.
> 
> Fixes: 23a890d493e3 ("net: mdio: Add the reset function for IPQ MDIO driver")
> Signed-off-by: Baruch Siach <baruch.siach@siklu.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH] net: mdio-ipq4019: add delay after clock enable

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Mon, 21 Feb 2022 13:45:57 +0200 you wrote:
> From: Baruch Siach <baruch.siach@siklu.com>
> 
> Experimentation shows that PHY detect might fail when the code attempts
> MDIO bus read immediately after clock enable. Add delay to stabilize the
> clock before bus access.
> 
> PHY detect failure started to show after commit 7590fc6f80ac ("net:
> mdio: Demote probed message to debug print") that removed coincidental
> delay between clock enable and bus access.
> 
> [...]

Here is the summary with links:
  - net: mdio-ipq4019: add delay after clock enable
    https://git.kernel.org/netdev/net/c/b6ad6261d277

You are awesome, thank you!
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