bootstd: Support bootmeths which can scan any partition

Some bootmeths support scanning a partition without a filesystem on it.
Add a flag to support this.

This will allow the ChromiumOS bootmeth to find kernel partition, which
are stored in a special format, without a filesystem.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/doc/develop/bootstd.rst b/doc/develop/bootstd.rst
index ec313653578..c01e0971dc8 100644
--- a/doc/develop/bootstd.rst
+++ b/doc/develop/bootstd.rst
@@ -677,11 +677,12 @@ Assuming the bootmeth is happy, or at least indicates that it is willing to try
 partition. If that works it tries to detect a file system. If that works then it
 calls the bootmeth device once more, this time to read the bootflow.
 
-Note: At present a filesystem is needed for the bootmeth to be called on block
-devices, simply because we don't have any examples where this is not the case.
-This feature can be added as needed. Note that sandbox is a special case, since
-in that case the host filesystem can be accessed even though the block device
-is NULL.
+Note: Normally a filesystem is needed for the bootmeth to be called on block
+devices, but bootmeths which don't need that can set the BOOTMETHF_ANY_PART
+flag to indicate that they can scan any partition. An example is the ChromiumOS
+bootmeth which can store a kernel in a raw partition. Note also that sandbox is
+a special case, since in that case the host filesystem can be accessed even
+though the block device is NULL.
 
 If we take the example of the `bootmeth_extlinux` driver, this call ends up at
 `extlinux_read_bootflow()`. It has the filesystem ready, so tries various