[libcamera-devel] [RFC PATCH] ipa: ipu3: Clear incoming parameter use flags

[Kieran Bingham]

The incoming params buffer may contain uninitialised data, or the
parameters of previously queued frames. Clearing the entire buffer
may be an expensive operation, and the kernel will only read from
structures which have their associated use-flag set.

It is the responsibility of the algorithms to set the use flags
accordingly for any data structure they update during prepare().

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

---

Yes, the commit message is the same as the comment before the line.
I felt the text was worthy of documenting the clearing of the flags, and
ensuring that it's documented in the code that the algorithms are
responsible for setting their use flag of any structure they modify.

Note that this is sent compile tested only, as it's something I noticed,
while writing documentation and wanted to check.

 src/ipa/ipu3/ipu3.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/ipa/ipu3/ipu3.cpp b/src/ipa/ipu3/ipu3.cpp
index c925cf642611..30d2a53903ec 100644
--- a/src/ipa/ipu3/ipu3.cpp
+++ b/src/ipa/ipu3/ipu3.cpp
@@ -457,6 +457,17 @@ void IPAIPU3::processControls([[maybe_unused]] unsigned int frame,
 
 void IPAIPU3::fillParams(unsigned int frame, ipu3_uapi_params *params)
 {
+	/*
+	 * The incoming params buffer may contain uninitialised data, or the
+	 * parameters of previously queued frames. Clearing the entire buffer
+	 * may be an expensive operation, and the kernel will only read from
+	 * structures which have their associated use-flag set.
+	 *
+	 * It is the responsibility of the algorithms to set the use flags
+	 * accordingly for any data structure they update during prepare().
+	 */
+	params->use = {};
+
 	for (auto const &algo : algorithms_)
 		algo->prepare(context_, params);
 
-- 
2.30.2