linux-kernel - [PATCH] media: dvb_ca_en50221: A bug is fixed for size write

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Date:   Thu, 18 Aug 2022 12:50:27 +0000
From:   YongSu Yoo <yongsuyoo0215@...il.com>
To:     mchehab@...nel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, yongsu.yoo@....com
Cc:     YongSu Yoo <yongsuyoo0215@...il.com>
Subject: [PATCH] media: dvb_ca_en50221: A bug is fixed for size write

Signed-off-by:Yongsu Yoo <yongsuyoo0215@...il.com>

The function of "dvb_ca_en50221_write_data" at source/drivers/media
/dvb-core/dvb_ca_en50221.c is used for two cases.
The first case is for writing APDU data in the function of
"dvb_ca_en50221_io_write" at source/drivers/media/dvb-core/
dvb_ca_en50221.c.
The second case is for writing the host link buf size on the
Command Register in the function of "dvb_ca_en50221_link_init"
at source/drivers/media/dvb-core/dvb_ca_en50221.c.
In the second case, there exists a bug like followings.
In the function of the "dvb_ca_en50221_link_init",
after a TV host calculates the host link buf_size,
the TV host writes the calculated host link buf_size on the
Size Register.
Accroding to the en50221 Spec (the page 60 of
https://dvb.org/wp-content/uploads/2020/02/En50221.V1.pdf),
before this writing operation, the "SW(CMDREG_SW)" flag in the
Command Register should be set. We can see this setting operation
in the function of the "dvb_ca_en50221_link_init" like below.
...
	if ((ret = ca->pub->write_cam_control(ca->pub, slot,
CTRLIF_COMMAND, IRQEN | CMDREG_SW)) != 0)
		return ret;
...
But, after that, the real writing operation is implemented using
the function of the "dvb_ca_en50221_write_data" in the function of
"dvb_ca_en50221_link_init", and the "dvb_ca_en50221_write_data"
includes the function of "ca->pub->write_cam_control",
and the function of the "ca->pub->write_cam_control" in the
function of the "dvb_ca_en50221_wrte_data" does not include
"CMDREG_SW" flag like below.
...
	if ((status = ca->pub->write_cam_control(ca->pub, slot,
CTRLIF_COMMAND, IRQEN | CMDREG_HC)) != 0)
...
In the above source code, we can see only the "IRQEN | CMDREG_HC",
but we cannot see the "CMDREG_SW".
The "CMDREG_SW" flag which was set in the function of the
"dvb_ca_en50221_link_init" was rollbacked by the follwoing function
of the "dvb_ca_en50221_write_data".
This is a bug. and this bug causes that the calculated host link buf_size
is not properly written in the CI module.
Through this patch, we fix this bug.
---
 drivers/media/dvb-core/dvb_ca_en50221.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c
index 15a08d8c69ef..13f249b0a080 100644
--- a/drivers/media/dvb-core/dvb_ca_en50221.c
+++ b/drivers/media/dvb-core/dvb_ca_en50221.c
@@ -187,7 +187,7 @@ static void dvb_ca_en50221_thread_wakeup(struct dvb_ca_private *ca);
 static int dvb_ca_en50221_read_data(struct dvb_ca_private *ca, int slot,
 				    u8 *ebuf, int ecount);
 static int dvb_ca_en50221_write_data(struct dvb_ca_private *ca, int slot,
-				     u8 *ebuf, int ecount);
+				     u8 *ebuf, int ecount, int size_write_flag);
 
 /**
  * findstr - Safely find needle in haystack.
@@ -370,7 +370,7 @@ static int dvb_ca_en50221_link_init(struct dvb_ca_private *ca, int slot)
 	ret = dvb_ca_en50221_wait_if_status(ca, slot, STATUSREG_FR, HZ / 10);
 	if (ret)
 		return ret;
-	ret = dvb_ca_en50221_write_data(ca, slot, buf, 2);
+	ret = dvb_ca_en50221_write_data(ca, slot, buf, 2, CMDREG_SW);
 	if (ret != 2)
 		return -EIO;
 	ret = ca->pub->write_cam_control(ca->pub, slot, CTRLIF_COMMAND, IRQEN);
@@ -778,11 +778,13 @@ static int dvb_ca_en50221_read_data(struct dvb_ca_private *ca, int slot,
  * @buf: The data in this buffer is treated as a complete link-level packet to
  *	 be written.
  * @bytes_write: Size of ebuf.
+ * @size_write_flag: A flag on Command Register which says whether the link size
+ * information will be writen or not. 
  *
  * return: Number of bytes written, or < 0 on error.
  */
 static int dvb_ca_en50221_write_data(struct dvb_ca_private *ca, int slot,
-				     u8 *buf, int bytes_write)
+				     u8 *buf, int bytes_write, int size_write_flag)
 {
 	struct dvb_ca_slot *sl = &ca->slot_info[slot];
 	int status;
@@ -817,7 +819,7 @@ static int dvb_ca_en50221_write_data(struct dvb_ca_private *ca, int slot,
 
 	/* OK, set HC bit */
 	status = ca->pub->write_cam_control(ca->pub, slot, CTRLIF_COMMAND,
-					    IRQEN | CMDREG_HC);
+					    IRQEN | CMDREG_HC | size_write_flag);
 	if (status)
 		goto exit;
 
@@ -1508,7 +1510,7 @@ static ssize_t dvb_ca_en50221_io_write(struct file *file,
 
 			mutex_lock(&sl->slot_lock);
 			status = dvb_ca_en50221_write_data(ca, slot, fragbuf,
-							   fraglen + 2);
+							   fraglen + 2, 0);
 			mutex_unlock(&sl->slot_lock);
 			if (status == (fraglen + 2)) {
 				written = 1;
-- 
2.17.1