media: vidtv: add a bridge driver

Digital TV devices consist of several independent hardware components
which are controlled by different drivers.
Each media device is controlled by a group of cooperating drivers with the
bridge driver as the main driver.

This patch adds a bridge driver for the Virtual Digital TV driver [vidtv].

The bridge driver binds to the other drivers, that is, vidtv_tuner and
vidtv_demod and implements the digital demux logic, providing userspace
with a MPEG Transport Stream.

The MPEG related code is split in the following way:

- vidtv_ts: code to work with MPEG TS packets, such as TS headers,
adaptation fields, PCR packets and NULL packets.

- vidtv_psi: this is the PSI generator.
PSI packets contain general information about a MPEG Transport Stream.
A PSI generator is needed so userspace apps can retrieve information
about the Transport Stream and eventually tune into a (dummy) channel.

Because the generator is implemented in a separate file, it can be
reused elsewhere in the media subsystem.

Currently vidtv supports working with 3 PSI tables:
PAT, PMT and SDT.

- vidtv_pes: implements the PES logic to convert encoder data into
MPEG TS packets. These can then be fed into a TS multiplexer and
eventually into userspace.

- vidtv_s302m: implements a S302M encoder to make it possible to
insert PCM audio data in the generated MPEG Transport Stream.

This shall enable passing an audio signal into userspace so it can be
decoded and played by media software.

- vidtv_channels: Implements a 'channel' abstraction

When vidtv boots, it will create some hardcoded channels:

Their services will be concatenated to populate the SDT.
Their programs will be concatenated to populate the PAT
For each program in the PAT, a PMT section will be created
The PMT section for a channel will be assigned its streams.
Every stream will have its corresponding encoder polled to produce TS
packets
These packets may be interleaved by the mux and then delivered to the
bridge

- vidtv_mux - Implements a MPEG TS mux, loosely based on the ffmpeg
implementation

The multiplexer is responsible for polling encoders,
interleaving packets, padding the resulting stream with NULL packets if
necessary and then delivering the resulting TS packets to the bridge
driver so it can feed the demux.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 89 insertions, 0 deletions

diff --git a/drivers/media/test-drivers/vidtv/vidtv_common.c b/drivers/media/test-drivers/vidtv/vidtv_common.c
new file mode 100644
index 000000000000..9093df32e0ab
--- /dev/null
+++ b/drivers/media/test-drivers/vidtv/vidtv_common.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The Virtual DVB test driver serves as a reference DVB driver and helps
+ * validate the existing APIs in the media subsystem. It can also aid
+ * developers working on userspace applications.
+ *
+ * Copyright (C) 2020 Daniel W. S. Almeida
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ":%s, %d: " fmt, __func__, __LINE__
+
+#include <linux/printk.h>
+#include <linux/ratelimit.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+#include "vidtv_common.h"
+
+/**
+ * vidtv_memcpy() - wrapper routine to be used by MPEG-TS
+ *	generator, in order to avoid going past the
+ *	output buffer.
+ * @to:	Starting element to where a MPEG-TS packet will
+ *	be copied.
+ * @to_offset:	Starting position of the @to buffer to be filled.
+ * @to_size:	Size of the @to buffer.
+ * @from:	Starting element of the buffer to be copied.
+ * @len:	Number of elements to be copy from @from buffer
+ *	into @to+ @to_offset buffer.
+ *
+ * Note:
+ *	Real digital TV demod drivers should not have memcpy
+ *	wrappers. We use it here because emulating MPEG-TS
+ *	generation at kernelspace requires some extra care.
+ *
+ * Return:
+ *	Returns the number of bytes written
+ */
+u32 vidtv_memcpy(void *to,
+		 size_t to_offset,
+		 size_t to_size,
+		 const void *from,
+		 size_t len)
+{
+	if (unlikely(to_offset + len > to_size)) {
+		pr_err_ratelimited("overflow detected, skipping. Try increasing the buffer size. Needed %lu, had %zu\n",
+				   to_offset + len,
+				   to_size);
+		return 0;
+	}
+
+	memcpy(to + to_offset, from, len);
+	return len;
+}
+
+/**
+ * vidtv_memset() - wrapper routine to be used by MPEG-TS
+ *	generator, in order to avoid going past the
+ *	output buffer.
+ * @to:	Starting element to set
+ * @to_offset:	Starting position of the @to buffer to be filled.
+ * @to_size:	Size of the @to buffer.
+ * @c:		The value to set the memory to.
+ * @len:	Number of elements to be copy from @from buffer
+ *	into @to+ @to_offset buffer.
+ *
+ * Note:
+ *	Real digital TV demod drivers should not have memset
+ *	wrappers. We use it here because emulating MPEG-TS
+ *	generation at kernelspace requires some extra care.
+ *
+ * Return:
+ *	Returns the number of bytes written
+ */
+u32 vidtv_memset(void *to,
+		 size_t to_offset,
+		 size_t to_size,
+		 const int c,
+		 size_t len)
+{
+	if (unlikely(to_offset + len > to_size)) {
+		pr_err_ratelimited("overflow detected, skipping. Try increasing the buffer size. Needed %lu, had %zu\n",
+				   to_offset + len,
+				   to_size);
+		return 0;
+	}
+
+	memset(to + to_offset, c, len);
+	return len;
+}