linux-kernel - [PATCH v2] staging: fbtft: Change udelay() to usleep

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Message-Id: <20260113210559.3020-1-gideonadjei.dev@gmail.com>
Date: Tue, 13 Jan 2026 13:05:59 -0800
From: Gideon Adjei <gideonadjei.dev@...il.com>
To: Andy Shevchenko <andy@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Abdun Nihaal <abdun.nihaal@...il.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Jianglei Nie <niejianglei2021@....com>,
	Matthew Wilcox <willy@...radead.org>,
	dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Gideon Adjei <gideonadjei.dev@...il.com>
Subject: [PATCH v2] staging: fbtft: Change udelay() to usleep_range()

Replace udelay() calls >= 100us with usleep_range() to avoid busy-waiting.

The delays are used in init_display() callbacks. These callbacks are
invoked by fbtft_probe_common() during the driver's probe path. the
probe path runs in process context which already uses sleeping APIs.
This makes usleep_range() safe to use in these situations.

Signed-off-by: Gideon Adjei <gideonadjei.dev@...il.com>
---
 drivers/staging/fbtft/fb_tinylcd.c   | 2 +-
 drivers/staging/fbtft/fb_upd161704.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/fbtft/fb_tinylcd.c b/drivers/staging/fbtft/fb_tinylcd.c
index 9469248f2c50..ee8d6b10374a 100644
--- a/drivers/staging/fbtft/fb_tinylcd.c
+++ b/drivers/staging/fbtft/fb_tinylcd.c
@@ -41,7 +41,7 @@ static int init_display(struct fbtft_par *par)
 		       0x00, 0x35, 0x33, 0x00, 0x00, 0x00);
 	write_reg(par, MIPI_DCS_SET_PIXEL_FORMAT, 0x55);
 	write_reg(par, MIPI_DCS_EXIT_SLEEP_MODE);
-	udelay(250);
+	usleep_range(250, 400);
 	write_reg(par, MIPI_DCS_SET_DISPLAY_ON);
 
 	return 0;
diff --git a/drivers/staging/fbtft/fb_upd161704.c b/drivers/staging/fbtft/fb_upd161704.c
index c680160d6380..aed5cc7cabde 100644
--- a/drivers/staging/fbtft/fb_upd161704.c
+++ b/drivers/staging/fbtft/fb_upd161704.c
@@ -32,7 +32,7 @@ static int init_display(struct fbtft_par *par)
 
 	/* oscillator start */
 	write_reg(par, 0x003A, 0x0001);	/*Oscillator 0: stop, 1: operation */
-	udelay(100);
+	usleep_range(100, 200);
 
 	/* y-setting */
 	write_reg(par, 0x0024, 0x007B);	/* amplitude setting */
@@ -60,7 +60,7 @@ static int init_display(struct fbtft_par *par)
 
 	/* Power supply setting */
 	write_reg(par, 0x0019, 0x0000);	/* DC/DC output setting */
-	udelay(200);
+	usleep_range(200, 400);
 	write_reg(par, 0x001A, 0x1000);	/* DC/DC frequency setting */
 	write_reg(par, 0x001B, 0x0023);	/* DC/DC rising setting */
 	write_reg(par, 0x001C, 0x0C01);	/* Regulator voltage setting */
-- 
2.34.1