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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jonathan Woithe <jwoithe@just42.net>,
        Johan Hovold <johan@kernel.org>
Subject: [PATCH 4.19 75/79] USB: serial: ch341: fix disabled rx timer on older devices
Date:   Tue, 13 Sep 2022 16:07:33 +0200
Message-Id: <20220913140352.508538258@linuxfoundation.org>
In-Reply-To: <20220913140348.835121645@linuxfoundation.org>
References: <20220913140348.835121645@linuxfoundation.org>
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From: Johan Hovold <johan@kernel.org>

commit 41ca302a697b64a3dab4676e01d0d11bb184737d upstream.

At least one older CH341 appears to have the RX timer enable bit
inverted so that setting it disables the RX timer and prevents the FIFO
from emptying until it is full.

Only set the RX timer enable bit for devices with version newer than
0x27 (even though this probably affects all pre-0x30 devices).

Reported-by: Jonathan Woithe <jwoithe@just42.net>
Tested-by: Jonathan Woithe <jwoithe@just42.net>
Link: https://lore.kernel.org/r/Ys1iPTfiZRWj2gXs@marvin.atrad.com.au
Fixes: 4e46c410e050 ("USB: serial: ch341: reinitialize chip on reconfiguration")
Cc: stable@vger.kernel.org      # 4.10
Signed-off-by: Johan Hovold <johan@kernel.org>
[ johan: backport to 5.4 ]
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/usb/serial/ch341.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -176,8 +176,12 @@ static int ch341_set_baudrate_lcr(struct
 	/*
 	 * CH341A buffers data until a full endpoint-size packet (32 bytes)
 	 * has been received unless bit 7 is set.
+	 *
+	 * At least one device with version 0x27 appears to have this bit
+	 * inverted.
 	 */
-	a |= BIT(7);
+	if (priv->version > 0x27)
+		a |= BIT(7);
 
 	r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x1312, a);
 	if (r)