linux-kernel - [PATCH v2] staging: sm750fb: replace magic number with jiffies timeout

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Message-ID: <20260127164816.91481-2-madhuananda18@gmail.com>
Date: Tue, 27 Jan 2026 16:48:16 +0000
From: Madhumitha Sundar <madhuananda18@...il.com>
To: gregkh@...uxfoundation.org
Cc: linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Madhumitha Sundar <madhuananda18@...il.com>
Subject: [PATCH v2] staging: sm750fb: replace magic number with jiffies timeout

The hardware wait loop in hw_sm750_de_wait used a hardcoded loop
counter (0x10000000), which depends on CPU speed and is unreliable.

Replace the loop counter with a jiffies-based timeout (1 second)
using time_before(). This ensures consistent delays across architectures.

Signed-off-by: Madhumitha Sundar <madhuananda18@...il.com>
---
Changes in v2:
 - Switched from loop counter to jiffies + cpu_relax() as requested by Greg KH.
---
 drivers/staging/sm750fb/sm750_hw.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/sm750fb/sm750_hw.c b/drivers/staging/sm750fb/sm750_hw.c
index ce46f240c..b24d27a77 100644
--- a/drivers/staging/sm750fb/sm750_hw.c
+++ b/drivers/staging/sm750fb/sm750_hw.c
@@ -523,19 +523,32 @@ int hw_sm750le_de_wait(void)
 
 int hw_sm750_de_wait(void)
 {
-	int i = 0x10000000;
+	/* Wait for 1 second (HZ) */
+	unsigned long timeout = jiffies + HZ;
 	unsigned int mask = SYSTEM_CTRL_DE_STATUS_BUSY |
 			    SYSTEM_CTRL_DE_FIFO_EMPTY |
 			    SYSTEM_CTRL_DE_MEM_FIFO_EMPTY;
+	unsigned int val;
 
-	while (i--) {
-		unsigned int val = peek32(SYSTEM_CTRL);
+	/* Run while Current Time is BEFORE the Deadline */
+	while (time_before(jiffies, timeout)) {
+		val = peek32(SYSTEM_CTRL);
 
+		/* If Not Busy (0) AND Buffers Empty (1), we are good */
 		if ((val & mask) ==
 		    (SYSTEM_CTRL_DE_FIFO_EMPTY | SYSTEM_CTRL_DE_MEM_FIFO_EMPTY))
 			return 0;
+
+		/* Polite pause to save power */
+		cpu_relax();
 	}
-	/* timeout error */
+
+	/* Final check in case we succeeded at the last millisecond */
+	val = peek32(SYSTEM_CTRL);
+	if ((val & mask) ==
+	    (SYSTEM_CTRL_DE_FIFO_EMPTY | SYSTEM_CTRL_DE_MEM_FIFO_EMPTY))
+		return 0;
+
 	return -1;
 }
 
-- 
2.43.0