Merge airlied/drm-next into drm-misc-next

Backmerge 4.15 and hdcp topic branch

Signed-off-by: Sean Paul <seanpaul@chromium.org>

3 files changed, 131 insertions, 7 deletions

diff --git a/Documentation/i2c/DMA-considerations b/Documentation/i2c/DMA-considerations
new file mode 100644
index 000000000000..966610aa4620
--- /dev/null
+++ b/Documentation/i2c/DMA-considerations
@@ -0,0 +1,67 @@
+=================
+Linux I2C and DMA
+=================
+
+Given that i2c is a low-speed bus, over which the majority of messages
+transferred are small, it is not considered a prime user of DMA access. At this
+time of writing, only 10% of I2C bus master drivers have DMA support
+implemented. And the vast majority of transactions are so small that setting up
+DMA for it will likely add more overhead than a plain PIO transfer.
+
+Therefore, it is *not* mandatory that the buffer of an I2C message is DMA safe.
+It does not seem reasonable to apply additional burdens when the feature is so
+rarely used. However, it is recommended to use a DMA-safe buffer if your
+message size is likely applicable for DMA. Most drivers have this threshold
+around 8 bytes (as of today, this is mostly an educated guess, however). For
+any message of 16 byte or larger, it is probably a really good idea. Please
+note that other subsystems you use might add requirements. E.g., if your
+I2C bus master driver is using USB as a bridge, then you need to have DMA
+safe buffers always, because USB requires it.
+
+Clients
+-------
+
+For clients, if you use a DMA safe buffer in i2c_msg, set the I2C_M_DMA_SAFE
+flag with it. Then, the I2C core and drivers know they can safely operate DMA
+on it. Note that using this flag is optional. I2C host drivers which are not
+updated to use this flag will work like before. And like before, they risk
+using an unsafe DMA buffer. To improve this situation, using I2C_M_DMA_SAFE in
+more and more clients and host drivers is the planned way forward. Note also
+that setting this flag makes only sense in kernel space. User space data is
+copied into kernel space anyhow. The I2C core makes sure the destination
+buffers in kernel space are always DMA capable. Also, when the core emulates
+SMBus transactions via I2C, the buffers for block transfers are DMA safe. Users
+of i2c_master_send() and i2c_master_recv() functions can now use DMA safe
+variants (i2c_master_send_dmasafe() and i2c_master_recv_dmasafe()) once they
+know their buffers are DMA safe. Users of i2c_transfer() must set the
+I2C_M_DMA_SAFE flag manually.
+
+Masters
+-------
+
+Bus master drivers wishing to implement safe DMA can use helper functions from
+the I2C core. One gives you a DMA-safe buffer for a given i2c_msg as long as a
+certain threshold is met::
+
+	dma_buf = i2c_get_dma_safe_msg_buf(msg, threshold_in_byte);
+
+If a buffer is returned, it is either msg->buf for the I2C_M_DMA_SAFE case or a
+bounce buffer. But you don't need to care about that detail, just use the
+returned buffer. If NULL is returned, the threshold was not met or a bounce
+buffer could not be allocated. Fall back to PIO in that case.
+
+In any case, a buffer obtained from above needs to be released. It ensures data
+is copied back to the message and a potentially used bounce buffer is freed::
+
+	i2c_release_dma_safe_msg_buf(msg, dma_buf);
+
+The bounce buffer handling from the core is generic and simple. It will always
+allocate a new bounce buffer. If you want a more sophisticated handling (e.g.
+reusing pre-allocated buffers), you are free to implement your own.
+
+Please also check the in-kernel documentation for details. The i2c-sh_mobile
+driver can be used as a reference example how to use the above helpers.
+
+Final note: If you plan to use DMA with I2C (or with anything else, actually)
+make sure you have CONFIG_DMA_API_DEBUG enabled during development. It can help
+you find various issues which can be complex to debug otherwise.
diff --git a/Documentation/i2c/dev-interface b/Documentation/i2c/dev-interface
index 5ff19447ac44..d04e6e4964ee 100644
--- a/Documentation/i2c/dev-interface
+++ b/Documentation/i2c/dev-interface
@@ -17,13 +17,16 @@ i2c-10, ...). All 256 minor device numbers are reserved for i2c.
 C example
 =========
 
-So let's say you want to access an i2c adapter from a C program. The
-first thing to do is "#include <linux/i2c-dev.h>". Please note that
-there are two files named "i2c-dev.h" out there, one is distributed
-with the Linux kernel and is meant to be included from kernel
-driver code, the other one is distributed with i2c-tools and is
-meant to be included from user-space programs. You obviously want
-the second one here.
+So let's say you want to access an i2c adapter from a C program.
+First, you need to include these two headers:
+
+  #include <linux/i2c-dev.h>
+  #include <i2c/smbus.h>
+
+(Please note that there are two files named "i2c-dev.h" out there. One is
+distributed with the Linux kernel and the other one is included in the
+source tree of i2c-tools. They used to be different in content but since 2012
+they're identical. You should use "linux/i2c-dev.h").
 
 Now, you have to decide which adapter you want to access. You should
 inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
diff --git a/Documentation/i2c/gpio-fault-injection b/Documentation/i2c/gpio-fault-injection
new file mode 100644
index 000000000000..e0c4f775e239
--- /dev/null
+++ b/Documentation/i2c/gpio-fault-injection
@@ -0,0 +1,54 @@
+Linux I2C fault injection
+=========================
+
+The GPIO based I2C bus master driver can be configured to provide fault
+injection capabilities. It is then meant to be connected to another I2C bus
+which is driven by the I2C bus master driver under test. The GPIO fault
+injection driver can create special states on the bus which the other I2C bus
+master driver should handle gracefully.
+
+Once the Kconfig option I2C_GPIO_FAULT_INJECTOR is enabled, there will be an
+'i2c-fault-injector' subdirectory in the Kernel debugfs filesystem, usually
+mounted at /sys/kernel/debug. There will be a separate subdirectory per GPIO
+driven I2C bus. Each subdirectory will contain files to trigger the fault
+injection. They will be described now along with their intended use-cases.
+
+"scl"
+-----
+
+By reading this file, you get the current state of SCL. By writing, you can
+change its state to either force it low or to release it again. So, by using
+"echo 0 > scl" you force SCL low and thus, no communication will be possible
+because the bus master under test will not be able to clock. It should detect
+the condition of SCL being unresponsive and report an error to the upper
+layers.
+
+"sda"
+-----
+
+By reading this file, you get the current state of SDA. By writing, you can
+change its state to either force it low or to release it again. So, by using
+"echo 0 > sda" you force SDA low and thus, data cannot be transmitted. The bus
+master under test should detect this condition and trigger a bus recovery (see
+I2C specification version 4, section 3.1.16) using the helpers of the Linux I2C
+core (see 'struct bus_recovery_info'). However, the bus recovery will not
+succeed because SDA is still pinned low until you manually release it again
+with "echo 1 > sda". A test with an automatic release can be done with the
+'incomplete_transfer' file.
+
+"incomplete_transfer"
+---------------------
+
+This file is write only and you need to write the address of an existing I2C
+client device to it. Then, a transfer to this device will be started, but it
+will stop at the ACK phase after the address of the client has been
+transmitted. Because the device will ACK its presence, this results in SDA
+being pulled low by the device while SCL is high. So, similar to the "sda" file
+above, the bus master under test should detect this condition and try a bus
+recovery. This time, however, it should succeed and the device should release
+SDA after toggling SCL. Please note: there are I2C client devices which detect
+a stuck SDA on their side and release it on their own after a few milliseconds.
+Also, there are external devices deglitching and monitoring the I2C bus. They
+can also detect a stuck SDA and will init a bus recovery on their own. If you
+want to implement bus recovery in a bus master driver, make sure you checked
+your hardware setup carefully before.