Linux I2C development
 help / color / mirror / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Chris Packham <chris.packham@alliedtelesis.co.nz>,
	Andi Shyti <andi.shyti@kernel.org>,
	stable@vger.kernel.org
Subject: [PATCH v1 1/1] i2c: mpc: Fix timeout calculations
Date: Thu, 18 Jun 2026 16:49:34 +0200	[thread overview]
Message-ID: <20260618144934.3249950-1-andriy.shevchenko@linux.intel.com> (raw)

ON the first glance the harmless cleanup of the driver does nothing bad.
However, as the operator precedence list states the '*' (multiplication)
and '/' division operators have order 5 with left-to-right associativity
the *= has order 17 and associativity right-to-left. It wouldn't not be
a problem to replace

	foo = foo * HZ / 1000000;

with

	foo *= HZ / 1000000;

if HZ constant is in Hertz. The problem is that in the Linux kernel HZ is
defined in jiffy units, which is order of magnitude smaller than a million.
That's why operator precedence has a crucial role here. Fix the regression
by reverting pre-optimized calculations.

Fixes: be40a3ae719f ("i2c: mpc: Use of_property_read_u32 instead of of_get_property")
Cc: stable@vger.kernel.org
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/i2c/busses/i2c-mpc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
index 28c5c5c1fb7a..a21fa45bd64c 100644
--- a/drivers/i2c/busses/i2c-mpc.c
+++ b/drivers/i2c/busses/i2c-mpc.c
@@ -844,7 +844,7 @@ static int fsl_i2c_probe(struct platform_device *op)
 					      "fsl,timeout", &mpc_ops.timeout);
 
 	if (!result) {
-		mpc_ops.timeout *= HZ / 1000000;
+		mpc_ops.timeout = mpc_ops.timeout * HZ / 1000000;
 		if (mpc_ops.timeout < 5)
 			mpc_ops.timeout = 5;
 	} else {
-- 
2.50.1


                 reply	other threads:[~2026-06-18 14:49 UTC|newest]

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20260618144934.3249950-1-andriy.shevchenko@linux.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=andi.shyti@kernel.org \
    --cc=chris.packham@alliedtelesis.co.nz \
    --cc=linux-i2c@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=stable@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox