Re: [PATCH V6 08/10] USB: f81232: fix read MSR strange value

From: Johan Hovold
Date: Tue Feb 17 2015 - 04:51:34 EST

On Mon, Feb 16, 2015 at 03:58:00PM +0800, Peter Hung wrote:
> When we use RS232 loopback, assume doing RTS change will cause
> CTS change, DTR change will cause DCD/DSR change too.
> Sometimes we got 7~4 bits of MSR changed but the 3~0 bits of
> MSR(delta) maybe not changed when set & get MCR fasterly.

I think you mean "rapidly" here.

> So we add more check not only UART_MSR_ANY_DELTA but also with
> comparing DCD/RI/DSR/CTS change with old value. Due to the state
> bit is always correct, we direct save msr when read.
> The following step to reproduce this problem with while loop step 1~4:
> 1. ioctl(fd, TIOCMSET, &data) to set RTS or DTR
> 2. ioctl(fd, TIOCMGET, &data) to read CTS or DCD/DSR state
> 3. ioctl(fd, TIOCMSET, &data) to unset RTS or DTR
> 4. ioctl(fd, TIOCMGET, &data) to read CTS or DCD/DSR state

Without having looked at this very closely; are you sure this is a
hardware issue and not related to the locking issues I pointed at in my
comments to tiocmset?

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