[PATCH/RFT] serial: prevent armada-370/xp uart buffer loss

[PATCH/RFT] serial: prevent armada-370/xp uart buffer loss

[Joshua Scott]

Switch to the "marvell,armada-38x-uart" driver variant to empty
the UART buffer before writing to the UART_LCR register.

Signed-off-by: Joshua Scott <joshua.scott@alliedtelesis.co.nz>
---

We have found that like the armada 38x, other Marvell SOCs can lose
characters when the UART_LCR register is written to without first
waiting for the buffer to empty.

We have observed this behaviour on the following Marvell switch SOCs:

 * 98DX323x
 * 98DX3333
 * 98DX4251

However, we do not currently have access to non-switch SOCs which share
the same parent device-tree.

The question we have is, should the fix be applied to the common
armada-370-xp device-tree, or should it be restricted to only affect the
SOCs listed above.

If anybody is able to check, we would like to find out if the issue
affects other armada-xp / armada-370 based SOCs.

The issue can be reproduced, if logging in using the serial port, with:
    resize && echo "hello world"

On affected devices, the first couple letters of "hello world" are
lost. On some SOCs this can be seen at 115200 baud, and on others
we have had to slow down to 9600 to see the issue.

Thank you,
Joshua Scott
---
 arch/arm/boot/dts/armada-370-xp.dtsi | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/boot/dts/armada-370-xp.dtsi b/arch/arm/boot/dts/armada-370-xp.dtsi
index c15f5e92f97f..9a956d1611ab 100644
--- a/arch/arm/boot/dts/armada-370-xp.dtsi
+++ b/arch/arm/boot/dts/armada-370-xp.dtsi
@@ -130,7 +130,7 @@
 			};
 
 			uart0: serial@12000 {
-				compatible = "snps,dw-apb-uart";
+				compatible = "marvell,armada-38x-uart";
 				reg = <0x12000 0x100>;
 				reg-shift = <2>;
 				interrupts = <41>;
@@ -140,7 +140,7 @@
 			};
 
 			uart1: serial@12100 {
-				compatible = "snps,dw-apb-uart";
+				compatible = "marvell,armada-38x-uart";
 				reg = <0x12100 0x100>;
 				reg-shift = <2>;
 				interrupts = <42>;
-- 
2.21.0


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Re: [PATCH/RFT] serial: prevent armada-370/xp uart buffer loss

[Andrew Lunn]

> The question we have is, should the fix be applied to the common
> armada-370-xp device-tree, or should it be restricted to only affect the
> SOCs listed above.
> 
> If anybody is able to check, we would like to find out if the issue
> affects other armada-xp / armada-370 based SOCs.
> 
> The issue can be reproduced, if logging in using the serial port, with:
>     resize && echo "hello world"

Hi Joshua

I tried this test out on a Marvell 370rd reference design. I tried
both 115200 and 9600 baud. I repeated the test maybe 10 times at each
speed. No dropped characters.

       Andrew

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