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From:   Luca Weiss <luca.weiss@fairphone.com>
Date:   Tue, 16 May 2023 08:52:43 +0200
Subject: [PATCH] docs: printk-formats: Clarify %*pb format parameters
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Message-Id: <20230516-printk-bitmap-v1-1-d5f810192a10@fairphone.com>
To:     Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Jonathan Corbet <corbet@lwn.net>
Cc:     ~postmarketos/upstreaming@lists.sr.ht, phone-devel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Luca Weiss <luca.weiss@fairphone.com>
Precedence: bulk

Since it's rather unusual for printk formats to require two parameters,
expand the documentation to clearly mention that in the printk format
for bitmaps.

As an extra example, for example from include/net/bluetooth/hci_core.h
we have a bitmap DECLARE_BITMAP(dev_flags, __HCI_NUM_FLAGS);
This can be printed with ("%*pb", __HCI_NUM_FLAGS, hdev->dev_flags)

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
---
This probably also applies to other printk formats but since this is the
only one so far I've used that requires two parameters I cannot really
help with the others.

Someone with more knowledge on the other more unusual format strings
could apply this to others also.
---
 Documentation/core-api/printk-formats.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index dfe7e75a71de..3cafb988d757 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -571,7 +571,9 @@ For printing bitmap and its derivatives such as cpumask and nodemask,
 %*pb outputs the bitmap with field width as the number of bits and %*pbl
 output the bitmap as range list with field width as the number of bits.
 
-The field width is passed by value, the bitmap is passed by reference.
+This requires two parameters, the field width (number of bits in the bitmap)
+passed by value and the bitmap passed by reference.
+
 Helper macros cpumask_pr_args() and nodemask_pr_args() are available to ease
 printing cpumask and nodemask.
 

---
base-commit: 16a8829130ca22666ac6236178a6233208d425c3
change-id: 20230516-printk-bitmap-bcffd77379ac

Best regards,
-- 
Luca Weiss <luca.weiss@fairphone.com>