[RFC PATCH 1/2] dma-buf/udmabuf: Introduce CONFIG_UDMABUF_SIZE_LIMIT_MBYTES

[Robert Mader <robert.mader@collabora.com>]

As udmabuf increasingly enjoys popularity - being used in projects like
libcamera, Gstreamer, Mesa and KWin - users more frequently encounter
cases where the current default size limit of 64MB is too low. Examples
include allocating video buffers at a 8K resolution - and even 4K is
affected when using non-subsampled video formats or high bit depths.

While the limit can already be changed via the kernel command line,
exposing it as a kernel config makes that easier and more discoverable
for distros. Thus let's do that.

Signed-off-by: Robert Mader <robert.mader@collabora.com>
---
 drivers/dma-buf/Kconfig   | 6 ++++++
 drivers/dma-buf/udmabuf.c | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index 7efc0f0d0712..35f0779cdc80 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -40,6 +40,12 @@ config UDMABUF
 	  A driver to let userspace turn memfd regions into dma-bufs.
 	  Qemu can use this to create host dmabufs for guest framebuffers.
 
+config UDMABUF_SIZE_LIMIT_MBYTES
+	int "Size limit in Mega Bytes"
+	default 64
+	help
+	  Maximum size of a udmabuf, in megabytes. Default is 64.
+
 config DMABUF_DEBUG
 	bool "DMA-BUF debug checks"
 	depends on DMA_SHARED_BUFFER
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index bced421c0d65..a83153326362 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -20,7 +20,11 @@ static int list_limit = 1024;
 module_param(list_limit, int, 0644);
 MODULE_PARM_DESC(list_limit, "udmabuf_create_list->count limit. Default is 1024.");
 
+#ifdef CONFIG_UDMABUF_SIZE_LIMIT_MBYTES
+static int size_limit_mb = CONFIG_UDMABUF_SIZE_LIMIT_MBYTES;
+#else
 static int size_limit_mb = 64;
+#endif
 module_param(size_limit_mb, int, 0644);
 MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is 64.");
 
-- 
2.55.0