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

From: Johan Hovold <johan@kernel.org>
To: Peter Hung <hpeter@gmail.com>
Cc: johan@kernel.org, gregkh@linuxfoundation.org,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	tom_tsai@fintek.com.tw, peter_hong@fintek.com.tw,
	Peter Hung <hpeter+linux_kernel@gmail.com>
Subject: Re: [PATCH V6 08/10] USB: f81232: fix read MSR strange value
Date: Tue, 17 Feb 2015 16:51:36 +0700	[thread overview]
Message-ID: <20150217095136.GU2551@localhost> (raw)
In-Reply-To: <1424073482-18164-9-git-send-email-hpeter+linux_kernel@gmail.com>

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?

Johan