[PATCH 1/3] media: dvb: add continuity error indicators for memory mapped buffers

[PATCH 1/3] media: dvb: add continuity error indicators for memory mapped buffers

[Mauro Carvalho Chehab]

While userspace can detect discontinuity errors, it is useful to
also let Kernelspace reporting discontinuity, as it can help to
identify if the data loss happened either at Kernel or userspace side.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 include/uapi/linux/dvb/dmx.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/include/uapi/linux/dvb/dmx.h b/include/uapi/linux/dvb/dmx.h
index 5f3c5a918f00..471c4afe738c 100644
--- a/include/uapi/linux/dvb/dmx.h
+++ b/include/uapi/linux/dvb/dmx.h
@@ -211,6 +211,32 @@ struct dmx_stc {
 	__u64 stc;
 };
 
+/**
+ * enum dmx_buffer_flags - DMX memory-mapped buffer flags
+ *
+ * @DMX_BUFFER_FLAG_HAD_CRC32_DISCARD:
+ *	Indicates that the Kernel discarded one or more frames due to wrong
+ *	CRC32 checksum.
+ * @DMX_BUFFER_FLAG_TEI:
+ * 	Indicates that the Kernel has detected a Transport Error indicator
+ *	(TEI) on a filtered pid.
+ * @DMX_BUFFER_PKT_COUNTER_MISMATCH:
+ * 	Indicates that the Kernel has detected a packet counter mismatch
+ *	on a filtered pid.
+ * @DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED:
+ * 	Indicates that the Kernel has detected one or more frame discontinuity.
+ * @DMX_BUFFER_FLAG_DISCONTINUITY_INDICATOR:
+ * 	Received at least one packet with a frame discontinuity indicator.
+ */
+
+enum dmx_buffer_flags {
+	DMX_BUFFER_FLAG_HAD_CRC32_DISCARD,
+	DMX_BUFFER_FLAG_TEI,
+	DMX_BUFFER_PKT_COUNTER_MISMATCH,
+	DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED,
+	DMX_BUFFER_FLAG_DISCONTINUITY_INDICATOR,
+};
+
 /**
  * struct dmx_buffer - dmx buffer info
  *
@@ -220,6 +246,11 @@ struct dmx_stc {
  *		offset from the start of the device memory for this plane,
  *		(or a "cookie" that should be passed to mmap() as offset)
  * @length:	size in bytes of the buffer
+ * @flags:	buffer flags as defined by &enum dmx_buffer_flags.
+ *		Filled only at &DMX_DQBUF. &DMX_QBUF should zero this field.
+ * @count:	monotonic counter for filled buffers. Helps to identify
+ *		data stream loses. Filled only at &DMX_DQBUF. &DMX_QBUF should
+ *		zero this field.
  *
  * Contains data exchanged by application and driver using one of the streaming
  * I/O methods.
@@ -229,6 +260,8 @@ struct dmx_buffer {
 	__u32			bytesused;
 	__u32			offset;
 	__u32			length;
+	__u32			flags;
+	__u32			count;
 };
 
 /**
-- 
2.14.3

[PATCH 2/3] media: dvb: update buffer mmaped flags and frame counter

[Mauro Carvalho Chehab]

Now that we have support for a buffer counter and for
error flags, update them at DMX_DQBUF.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 drivers/media/dvb-core/dmxdev.c    | 11 +++--
 drivers/media/dvb-core/dvb_demux.c | 95 ++++++++++++++++++++++++--------------
 drivers/media/dvb-core/dvb_vb2.c   | 14 +++++-
 include/media/demux.h              | 11 +++--
 include/media/dvb_vb2.h            | 15 +++++-
 5 files changed, 101 insertions(+), 45 deletions(-)

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 41cacb7b5703..03485a706929 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -399,10 +399,12 @@ static int dvb_dmxdev_section_callback(const u8 *buffer1, size_t buffer1_len,
 	dprintk("section callback %*ph\n", 6, buffer1);
 	if (dvb_vb2_is_streaming(&dmxdevfilter->vb2_ctx)) {
 		ret = dvb_vb2_fill_buffer(&dmxdevfilter->vb2_ctx,
-					  buffer1, buffer1_len);
+					  buffer1, buffer1_len,
+					  &filter->buffer_flags);
 		if (ret == buffer1_len)
 			ret = dvb_vb2_fill_buffer(&dmxdevfilter->vb2_ctx,
-						  buffer2, buffer2_len);
+						  buffer2, buffer2_len,
+						  &filter->buffer_flags);
 	} else {
 		ret = dvb_dmxdev_buffer_write(&dmxdevfilter->buffer,
 					      buffer1, buffer1_len);
@@ -451,9 +453,10 @@ static int dvb_dmxdev_ts_callback(const u8 *buffer1, size_t buffer1_len,
 	}
 
 	if (dvb_vb2_is_streaming(ctx)) {
-		ret = dvb_vb2_fill_buffer(ctx, buffer1, buffer1_len);
+		ret = dvb_vb2_fill_buffer(ctx, buffer1, buffer1_len, NULL);
 		if (ret == buffer1_len)
-			ret = dvb_vb2_fill_buffer(ctx, buffer2, buffer2_len);
+			ret = dvb_vb2_fill_buffer(ctx, buffer2, buffer2_len,
+						  NULL);
 	} else {
 		if (buffer->error) {
 			spin_unlock(&dmxdevfilter->dev->lock);
diff --git a/drivers/media/dvb-core/dvb_demux.c b/drivers/media/dvb-core/dvb_demux.c
index 210eed0269b0..6b82281660ca 100644
--- a/drivers/media/dvb-core/dvb_demux.c
+++ b/drivers/media/dvb-core/dvb_demux.c
@@ -55,6 +55,15 @@ MODULE_PARM_DESC(dvb_demux_feed_err_pkts,
 		dprintk(x);				\
 } while (0)
 
+#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
+#  define dprintk_sect_loss(x...) dprintk(x)
+#else
+#  define dprintk_sect_loss(x...)
+#endif
+
+#define set_buf_flags(__feed, __flag) \
+	do { (__feed)->filter->filter.buffer_flags |= (__flag); } while (0)
+
 /******************************************************************************
  * static inlined helper functions
  ******************************************************************************/
@@ -104,24 +113,22 @@ static inline int dvb_dmx_swfilter_payload(struct dvb_demux_feed *feed,
 {
 	int count = payload(buf);
 	int p;
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
 	int ccok;
 	u8 cc;
-#endif
 
 	if (count == 0)
 		return -1;
 
 	p = 188 - count;
 
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
 	cc = buf[3] & 0x0f;
 	ccok = ((feed->cc + 1) & 0x0f) == cc;
 	feed->cc = cc;
-	if (!ccok)
-		dprintk("missed packet: %d instead of %d!\n",
-			cc, (feed->cc + 1) & 0x0f);
-#endif
+	if (!ccok) {
+		set_buf_flags(feed, DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+		dprintk_sect_loss("missed packet: %d instead of %d!\n",
+				  cc, (feed->cc + 1) & 0x0f);
+	}
 
 	if (buf[1] & 0x40)	// PUSI ?
 		feed->peslen = 0xfffa;
@@ -169,8 +176,10 @@ static inline int dvb_dmx_swfilter_section_feed(struct dvb_demux_feed *feed)
 	if (sec->check_crc) {
 		section_syntax_indicator = ((sec->secbuf[1] & 0x80) != 0);
 		if (section_syntax_indicator &&
-		    demux->check_crc32(feed, sec->secbuf, sec->seclen))
+		    demux->check_crc32(feed, sec->secbuf, sec->seclen)) {
+			set_buf_flags(feed, DMX_BUFFER_FLAG_HAD_CRC32_DISCARD);
 			return -1;
+		}
 	}
 
 	do {
@@ -187,7 +196,6 @@ static void dvb_dmx_swfilter_section_new(struct dvb_demux_feed *feed)
 {
 	struct dmx_section_feed *sec = &feed->feed.sec;
 
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
 	if (sec->secbufp < sec->tsfeedp) {
 		int n = sec->tsfeedp - sec->secbufp;
 
@@ -197,12 +205,13 @@ static void dvb_dmx_swfilter_section_new(struct dvb_demux_feed *feed)
 		 * but just first and last.
 		 */
 		if (sec->secbuf[0] != 0xff || sec->secbuf[n - 1] != 0xff) {
-			dprintk("section ts padding loss: %d/%d\n",
-			       n, sec->tsfeedp);
-			dprintk("pad data: %*ph\n", n, sec->secbuf);
+			set_buf_flags(feed,
+				      DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+			dprintk_sect_loss("section ts padding loss: %d/%d\n",
+					  n, sec->tsfeedp);
+			dprintk_sect_loss("pad data: %*ph\n", n, sec->secbuf);
 		}
 	}
-#endif
 
 	sec->tsfeedp = sec->secbufp = sec->seclen = 0;
 	sec->secbuf = sec->secbuf_base;
@@ -237,11 +246,10 @@ static int dvb_dmx_swfilter_section_copy_dump(struct dvb_demux_feed *feed,
 		return 0;
 
 	if (sec->tsfeedp + len > DMX_MAX_SECFEED_SIZE) {
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
-		dprintk("section buffer full loss: %d/%d\n",
-			sec->tsfeedp + len - DMX_MAX_SECFEED_SIZE,
-			DMX_MAX_SECFEED_SIZE);
-#endif
+		set_buf_flags(feed, DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+		dprintk_sect_loss("section buffer full loss: %d/%d\n",
+				  sec->tsfeedp + len - DMX_MAX_SECFEED_SIZE,
+				  DMX_MAX_SECFEED_SIZE);
 		len = DMX_MAX_SECFEED_SIZE - sec->tsfeedp;
 	}
 
@@ -269,12 +277,13 @@ static int dvb_dmx_swfilter_section_copy_dump(struct dvb_demux_feed *feed,
 		sec->seclen = seclen;
 		sec->crc_val = ~0;
 		/* dump [secbuf .. secbuf+seclen) */
-		if (feed->pusi_seen)
+		if (feed->pusi_seen) {
 			dvb_dmx_swfilter_section_feed(feed);
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
-		else
-			dprintk("pusi not seen, discarding section data\n");
-#endif
+		} else {
+			set_buf_flags(feed,
+				      DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+			dprintk_sect_loss("pusi not seen, discarding section data\n");
+		}
 		sec->secbufp += seclen;	/* secbufp and secbuf moving together is */
 		sec->secbuf += seclen;	/* redundant but saves pointer arithmetic */
 	}
@@ -307,18 +316,22 @@ static int dvb_dmx_swfilter_section_packet(struct dvb_demux_feed *feed,
 	}
 
 	if (!ccok || dc_i) {
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
-		if (dc_i)
-			dprintk("%d frame with disconnect indicator\n",
+		if (dc_i) {
+			set_buf_flags(feed,
+				      DMX_BUFFER_FLAG_DISCONTINUITY_INDICATOR);
+			dprintk_sect_loss("%d frame with disconnect indicator\n",
 				cc);
-		else
-			dprintk("discontinuity: %d instead of %d. %d bytes lost\n",
+		} else {
+			set_buf_flags(feed,
+				      DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+			dprintk_sect_loss("discontinuity: %d instead of %d. %d bytes lost\n",
 				cc, (feed->cc + 1) & 0x0f, count + 4);
+		}
 		/*
-		 * those bytes under sume circumstances will again be reported
+		 * those bytes under some circumstances will again be reported
 		 * in the following dvb_dmx_swfilter_section_new
 		 */
-#endif
+
 		/*
 		 * Discontinuity detected. Reset pusi_seen to
 		 * stop feeding of suspicious data until next PUSI=1 arrives
@@ -326,6 +339,7 @@ static int dvb_dmx_swfilter_section_packet(struct dvb_demux_feed *feed,
 		 * FIXME: does it make sense if the MPEG-TS is the one
 		 *	reporting discontinuity?
 		 */
+
 		feed->pusi_seen = false;
 		dvb_dmx_swfilter_section_new(feed);
 	}
@@ -346,10 +360,11 @@ static int dvb_dmx_swfilter_section_packet(struct dvb_demux_feed *feed,
 			dvb_dmx_swfilter_section_copy_dump(feed, after,
 							   after_len);
 		}
-#ifdef CONFIG_DVB_DEMUX_SECTION_LOSS_LOG
-		else if (count > 0)
-			dprintk("PUSI=1 but %d bytes lost\n", count);
-#endif
+		else if (count > 0) {
+			set_buf_flags(feed,
+				      DMX_BUFFER_FLAG_DISCONTINUITY_DETECTED);
+			dprintk_sect_loss("PUSI=1 but %d bytes lost\n", count);
+		}
 	} else {
 		/* PUSI=0 (is not set), no section boundary */
 		dvb_dmx_swfilter_section_copy_dump(feed, &buf[p], count);
@@ -430,6 +445,11 @@ static void dvb_dmx_swfilter_packet(struct dvb_demux *demux, const u8 *buf)
 	}
 
 	if (buf[1] & 0x80) {
+		list_for_each_entry(feed, &demux->feed_list, list_head) {
+			if ((feed->pid != pid) && (feed->pid != 0x2000))
+				continue;
+			set_buf_flags(feed, DMX_BUFFER_FLAG_TEI);
+		}
 		dprintk_tscheck("TEI detected. PID=0x%x data1=0x%x\n",
 				pid, buf[1]);
 		/* data in this packet can't be trusted - drop it unless
@@ -445,6 +465,13 @@ static void dvb_dmx_swfilter_packet(struct dvb_demux *demux, const u8 *buf)
 						(demux->cnt_storage[pid] + 1) & 0xf;
 
 				if ((buf[3] & 0xf) != demux->cnt_storage[pid]) {
+					list_for_each_entry(feed, &demux->feed_list, list_head) {
+						if ((feed->pid != pid) && (feed->pid != 0x2000))
+							continue;
+						set_buf_flags(feed,
+							      DMX_BUFFER_PKT_COUNTER_MISMATCH);
+					}
+
 					dprintk_tscheck("TS packet counter mismatch. PID=0x%x expected 0x%x got 0x%x\n",
 							pid, demux->cnt_storage[pid],
 							buf[3] & 0xf);
diff --git a/drivers/media/dvb-core/dvb_vb2.c b/drivers/media/dvb-core/dvb_vb2.c
index 889abf9becd8..a674e8cce937 100644
--- a/drivers/media/dvb-core/dvb_vb2.c
+++ b/drivers/media/dvb-core/dvb_vb2.c
@@ -256,7 +256,8 @@ int dvb_vb2_is_streaming(struct dvb_vb2_ctx *ctx)
 }
 
 int dvb_vb2_fill_buffer(struct dvb_vb2_ctx *ctx,
-			const unsigned char *src, int len)
+			const unsigned char *src, int len,
+			enum dmx_buffer_flags *buffer_flags)
 {
 	unsigned long flags = 0;
 	void *vbuf = NULL;
@@ -283,6 +284,12 @@ int dvb_vb2_fill_buffer(struct dvb_vb2_ctx *ctx,
 
 			ctx->buf = list_entry(ctx->dvb_q.next,
 					      struct dvb_buffer, list);
+			if (buffer_flags) {
+				ctx->flags = *buffer_flags;
+				*buffer_flags = 0;
+			} else {
+				ctx->flags = 0;
+			}
 			ctx->remain = vb2_plane_size(&ctx->buf->vb, 0);
 			ctx->offset = 0;
 		}
@@ -402,7 +409,10 @@ int dvb_vb2_dqbuf(struct dvb_vb2_ctx *ctx, struct dmx_buffer *b)
 		dprintk(1, "[%s] errno=%d\n", ctx->name, ret);
 		return ret;
 	}
-	dprintk(5, "[%s] index=%d\n", ctx->name, b->index);
+	b->count = ctx->count++;
+	b->flags = ctx->flags;
+	dprintk(5, "[%s] index=%d, count=%d, flags=%d\n",
+		ctx->name, b->index, ctx->count, ctx->flags);
 
 	return 0;
 }
diff --git a/include/media/demux.h b/include/media/demux.h
index c4df6cee48e6..95b643f54d26 100644
--- a/include/media/demux.h
+++ b/include/media/demux.h
@@ -117,7 +117,9 @@ struct dmx_ts_feed {
  *		  specified by @filter_value that will be used on the filter
  *		  match logic.
  * @filter_mode:  Contains a 16 bytes (128 bits) filter mode.
- * @parent:	  Pointer to struct dmx_section_feed.
+ * @buffer_flags: Buffer flags used to report discontinuity users via DVB
+ *		  memory mapped API, as defined by &enum dmx_buffer_flags.
+ * @parent:	  Back-pointer to struct dmx_section_feed.
  * @priv:	  Pointer to private data of the API client.
  *
  *
@@ -130,8 +132,11 @@ struct dmx_section_filter {
 	u8 filter_value[DMX_MAX_FILTER_SIZE];
 	u8 filter_mask[DMX_MAX_FILTER_SIZE];
 	u8 filter_mode[DMX_MAX_FILTER_SIZE];
-	struct dmx_section_feed *parent; /* Back-pointer */
-	void *priv; /* Pointer to private data of the API client */
+	struct dmx_section_feed *parent;
+
+	enum dmx_buffer_flags buffer_flags;
+
+	void *priv;
 };
 
 /**
diff --git a/include/media/dvb_vb2.h b/include/media/dvb_vb2.h
index af9aeccb0b41..1b2c6bc587af 100644
--- a/include/media/dvb_vb2.h
+++ b/include/media/dvb_vb2.h
@@ -85,6 +85,12 @@ struct dvb_buffer {
  * @nonblocking:
  *		If different than zero, device is operating on non-blocking
  *		mode.
+ * @flags:	buffer flags as defined by &enum dmx_buffer_flags.
+ *		Filled only at &DMX_DQBUF. &DMX_QBUF should zero this field.
+ * @count:	monotonic counter for filled buffers. Helps to identify
+ *		data stream loses. Filled only at &DMX_DQBUF. &DMX_QBUF should
+ *		zero this field.
+ *
  * @name:	name of the device type. Currently, it can either be
  *		"dvr" or "demux_filter".
  */
@@ -100,6 +106,10 @@ struct dvb_vb2_ctx {
 	int	buf_siz;
 	int	buf_cnt;
 	int	nonblocking;
+
+	enum dmx_buffer_flags flags;
+	u32	count;
+
 	char	name[DVB_VB2_NAME_MAX + 1];
 };
 
@@ -114,7 +124,7 @@ static inline int dvb_vb2_release(struct dvb_vb2_ctx *ctx)
 	return 0;
 };
 #define dvb_vb2_is_streaming(ctx) (0)
-#define dvb_vb2_fill_buffer(ctx, file, wait) (0)
+#define dvb_vb2_fill_buffer(ctx, file, wait, flags) (0)
 
 static inline unsigned int dvb_vb2_poll(struct dvb_vb2_ctx *ctx,
 					struct file *file,
@@ -155,7 +165,8 @@ int dvb_vb2_is_streaming(struct dvb_vb2_ctx *ctx);
  * @len:	number of bytes to be copied from @src
  */
 int dvb_vb2_fill_buffer(struct dvb_vb2_ctx *ctx,
-			const unsigned char *src, int len);
+			const unsigned char *src, int len,
+			enum dmx_buffer_flags *buffer_flags);
 
 /**
  * dvb_vb2_poll - Wrapper to vb2_core_streamon() for Digital TV
-- 
2.14.3

[PATCH 3/3] media: dmxdev: Fix the logic that enables DMA mmap support

[Mauro Carvalho Chehab]

Some conditions required for DVB mmap support to work are reversed.
Also, the logic is not too clear.

So, improve the logic, making it easier to be handled.

PS.: I'm pretty sure that I fixed it while testing, but, somehow,
the change got lost.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
---
 drivers/media/dvb-core/dmxdev.c | 75 +++++++++++++++++++++++------------------
 include/media/dmxdev.h          |  2 ++
 2 files changed, 44 insertions(+), 33 deletions(-)

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index 03485a706929..94682bb8d08e 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -128,11 +128,7 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
 	struct dvb_device *dvbdev = file->private_data;
 	struct dmxdev *dmxdev = dvbdev->priv;
 	struct dmx_frontend *front;
-#ifndef CONFIG_DVB_MMAP
 	bool need_ringbuffer = false;
-#else
-	const bool need_ringbuffer = true;
-#endif
 
 	dprintk("%s\n", __func__);
 
@@ -144,17 +140,31 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
 		return -ENODEV;
 	}
 
-#ifndef CONFIG_DVB_MMAP
+	dmxdev->may_do_mmap = 0;
+
+	/*
+	 * The logic here is a little tricky due to the ifdef.
+	 *
+	 * The ringbuffer is used for both read and mmap.
+	 *
+	 * It is not needed, however, on two situations:
+	 * 	- Write devices (access with O_WRONLY);
+	 *	- For duplex device nodes, opened with O_RDWR.
+	 */
+
 	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
 		need_ringbuffer = true;
-#else
-	if ((file->f_flags & O_ACCMODE) == O_RDWR) {
+	else if ((file->f_flags & O_ACCMODE) == O_RDWR) {
 		if (!(dmxdev->capabilities & DMXDEV_CAP_DUPLEX)) {
+#ifdef CONFIG_DVB_MMAP
+			dmxdev->may_do_mmap = 1;
+			need_ringbuffer = true;
+#else
 			mutex_unlock(&dmxdev->mutex);
 			return -EOPNOTSUPP;
+#endif
 		}
 	}
-#endif
 
 	if (need_ringbuffer) {
 		void *mem;
@@ -169,8 +179,9 @@ static int dvb_dvr_open(struct inode *inode, struct file *file)
 			return -ENOMEM;
 		}
 		dvb_ringbuffer_init(&dmxdev->dvr_buffer, mem, DVR_BUFFER_SIZE);
-		dvb_vb2_init(&dmxdev->dvr_vb2_ctx, "dvr",
-			     file->f_flags & O_NONBLOCK);
+		if (dmxdev->may_do_mmap)
+			dvb_vb2_init(&dmxdev->dvr_vb2_ctx, "dvr",
+				     file->f_flags & O_NONBLOCK);
 		dvbdev->readers--;
 	}
 
@@ -200,11 +211,6 @@ static int dvb_dvr_release(struct inode *inode, struct file *file)
 {
 	struct dvb_device *dvbdev = file->private_data;
 	struct dmxdev *dmxdev = dvbdev->priv;
-#ifndef CONFIG_DVB_MMAP
-	bool need_ringbuffer = false;
-#else
-	const bool need_ringbuffer = true;
-#endif
 
 	mutex_lock(&dmxdev->mutex);
 
@@ -213,15 +219,14 @@ static int dvb_dvr_release(struct inode *inode, struct file *file)
 		dmxdev->demux->connect_frontend(dmxdev->demux,
 						dmxdev->dvr_orig_fe);
 	}
-#ifndef CONFIG_DVB_MMAP
-	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
-		need_ringbuffer = true;
-#endif
 
-	if (need_ringbuffer) {
-		if (dvb_vb2_is_streaming(&dmxdev->dvr_vb2_ctx))
-			dvb_vb2_stream_off(&dmxdev->dvr_vb2_ctx);
-		dvb_vb2_release(&dmxdev->dvr_vb2_ctx);
+	if (((file->f_flags & O_ACCMODE) == O_RDONLY) ||
+	    dmxdev->may_do_mmap) {
+		if (dmxdev->may_do_mmap) {
+			if (dvb_vb2_is_streaming(&dmxdev->dvr_vb2_ctx))
+				dvb_vb2_stream_off(&dmxdev->dvr_vb2_ctx);
+			dvb_vb2_release(&dmxdev->dvr_vb2_ctx);
+		}
 		dvbdev->readers++;
 		if (dmxdev->dvr_buffer.data) {
 			void *mem = dmxdev->dvr_buffer.data;
@@ -805,6 +810,12 @@ static int dvb_demux_open(struct inode *inode, struct file *file)
 	mutex_init(&dmxdevfilter->mutex);
 	file->private_data = dmxdevfilter;
 
+#ifdef CONFIG_DVB_MMAP
+	dmxdev->may_do_mmap = 1;
+#else
+	dmxdev->may_do_mmap = 0;
+#endif
+
 	dvb_ringbuffer_init(&dmxdevfilter->buffer, NULL, 8192);
 	dvb_vb2_init(&dmxdevfilter->vb2_ctx, "demux_filter",
 		     file->f_flags & O_NONBLOCK);
@@ -1209,6 +1220,9 @@ static int dvb_demux_mmap(struct file *file, struct vm_area_struct *vma)
 	struct dmxdev *dmxdev = dmxdevfilter->dev;
 	int ret;
 
+	if (!dmxdev->may_do_mmap)
+		return -EOPNOTSUPP;
+
 	if (mutex_lock_interruptible(&dmxdev->mutex))
 		return -ERESTARTSYS;
 
@@ -1325,11 +1339,6 @@ static unsigned int dvb_dvr_poll(struct file *file, poll_table *wait)
 	struct dvb_device *dvbdev = file->private_data;
 	struct dmxdev *dmxdev = dvbdev->priv;
 	unsigned int mask = 0;
-#ifndef CONFIG_DVB_MMAP
-	bool need_ringbuffer = false;
-#else
-	const bool need_ringbuffer = true;
-#endif
 
 	dprintk("%s\n", __func__);
 
@@ -1340,11 +1349,8 @@ static unsigned int dvb_dvr_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &dmxdev->dvr_buffer.queue, wait);
 
-#ifndef CONFIG_DVB_MMAP
-	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
-		need_ringbuffer = true;
-#endif
-	if (need_ringbuffer) {
+	if (((file->f_flags & O_ACCMODE) == O_RDONLY) ||
+	    dmxdev->may_do_mmap) {
 		if (dmxdev->dvr_buffer.error)
 			mask |= (POLLIN | POLLRDNORM | POLLPRI | POLLERR);
 
@@ -1363,6 +1369,9 @@ static int dvb_dvr_mmap(struct file *file, struct vm_area_struct *vma)
 	struct dmxdev *dmxdev = dvbdev->priv;
 	int ret;
 
+	if (!dmxdev->may_do_mmap)
+		return -EOPNOTSUPP;
+
 	if (dmxdev->exit)
 		return -ENODEV;
 
diff --git a/include/media/dmxdev.h b/include/media/dmxdev.h
index 2f5cb2c7b6a7..baafa3b8aca4 100644
--- a/include/media/dmxdev.h
+++ b/include/media/dmxdev.h
@@ -163,6 +163,7 @@ struct dmxdev_filter {
  * @demux:		pointer to &struct dmx_demux.
  * @filternum:		number of filters.
  * @capabilities:	demux capabilities as defined by &enum dmx_demux_caps.
+ * @may_do_mmap:	flag used to indicate if the device may do mmap.
  * @exit:		flag to indicate that the demux is being released.
  * @dvr_orig_fe:	pointer to &struct dmx_frontend.
  * @dvr_buffer:		embedded &struct dvb_ringbuffer for DVB output.
@@ -180,6 +181,7 @@ struct dmxdev {
 	int filternum;
 	int capabilities;
 
+	unsigned int may_do_mmap:1;
 	unsigned int exit:1;
 #define DMXDEV_CAP_DUPLEX 1
 	struct dmx_frontend *dvr_orig_fe;
-- 
2.14.3