4.16 OMAP serial transmit corruption?

[Vignesh R]

On Tuesday 17 April 2018 02:50 PM, Vignesh R wrote:
> 
> 
> On Monday 16 April 2018 09:15 PM, Tony Lindgren wrote:
>> * Russell King - ARM Linux <linux at armlinux.org.uk> [180416 15:19]:
>>> Hi,
>>>
>>> I'm not entirely sure what's going on, but I see corrupted characters
>>> with the serial console on the OMAP4430 SDP board.  During boot,
>>> everything seems fine, the problem appears to be userspace output.
>>>
>>> For example, if I edit a file, then quit vi:
>>>
>>> :q■■%■■B■■Z■root at omap-4430sdp:~#
>>
>> I don't think I've seen that one. What I've seen few times is
>> typing a key on the serial console echoing back the previous
>> character typed while the new character won't get displayed
>> until hitting keyboard again. Only rebooting the device seems
>> to solve this. This is with 4430 ES2.3 revision.
>>
>> I wonder if we're missing some parts of errata i202 handling
>> in omap_8250_mdr1_errataset()?
>>

I wonder if the extra read of MDR1 register at the beginning of
omap_8250_mdr1_errataset() compared to omap-serial is the issue.
errata i202 says access to MDR1 can cause data corruption. 
Assuming both reads and writes can cause glitch then, that read
is not following advisory:

I don't have SDP board so, could you verify if below diff helps:


diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 6aaa84355fd1..8ab9d0a1b1eb 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -163,11 +163,6 @@ static void omap_8250_mdr1_errataset(struct uart_8250_port *up,
                                     struct omap8250_priv *priv)
 {
        u8 timeout = 255;
-       u8 old_mdr1;
-
-       old_mdr1 = serial_in(up, UART_OMAP_MDR1);
-       if (old_mdr1 == priv->mdr1)
-               return;
 
        serial_out(up, UART_OMAP_MDR1, priv->mdr1);
        udelay(2);



-- 
Regards
Vignesh