DriverDev-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Linus Walleij <linus.walleij@linaro.org>
To: gregkh@linuxfoundation.org
Cc: devel@driverdev.osuosl.org,
	Linus Walleij <linus.walleij@linaro.org>,
	Mark Brown <broonie@kernel.org>
Subject: [PATCH] staging: fbtft: Do not hardcode SPI CS polarity inversion
Date: Thu,  5 Dec 2019 00:32:30 +0100
Message-ID: <20191204233230.22309-1-linus.walleij@linaro.org> (raw)

The current use of the mode flag SPI_CS_HIGH is fragile: it
overwrites anything already assigned by the SPI core.

Assign ^= SPI_CS_HIGH since we might be active high
already, and that is usually the case with GPIOs used
for chip select, even if they are in practice active low.

Add a comment clarifying why ^= SPI_CS_HIGH is the right
choice here.

Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/staging/fbtft/fb_uc1611.c    | 12 +++++++++---
 drivers/staging/fbtft/fb_watterott.c | 13 ++++++++++---
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/fbtft/fb_uc1611.c b/drivers/staging/fbtft/fb_uc1611.c
index e763205e9e4f..f61e373c75e9 100644
--- a/drivers/staging/fbtft/fb_uc1611.c
+++ b/drivers/staging/fbtft/fb_uc1611.c
@@ -63,11 +63,17 @@ static int init_display(struct fbtft_par *par)
 {
 	int ret;
 
-	/* Set CS active high */
-	par->spi->mode |= SPI_CS_HIGH;
+	/*
+	 * Set CS active inverse polarity: just setting SPI_CS_HIGH does not
+	 * work with GPIO based chip selects that are logically active high
+	 * but inverted inside the GPIO library, so enforce inverted
+	 * semantics.
+	 */
+	par->spi->mode ^= SPI_CS_HIGH;
 	ret = spi_setup(par->spi);
 	if (ret) {
-		dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
+		dev_err(par->info->device,
+			"Could not set inverse CS polarity\n");
 		return ret;
 	}
 
diff --git a/drivers/staging/fbtft/fb_watterott.c b/drivers/staging/fbtft/fb_watterott.c
index 27cc8eabcbe9..76b25df376b8 100644
--- a/drivers/staging/fbtft/fb_watterott.c
+++ b/drivers/staging/fbtft/fb_watterott.c
@@ -150,10 +150,17 @@ static int init_display(struct fbtft_par *par)
 
 	/* enable SPI interface by having CS and MOSI low during reset */
 	save_mode = par->spi->mode;
-	par->spi->mode |= SPI_CS_HIGH;
-	ret = spi_setup(par->spi); /* set CS inactive low */
+	/*
+	 * Set CS active inverse polarity: just setting SPI_CS_HIGH does not
+	 * work with GPIO based chip selects that are logically active high
+	 * but inverted inside the GPIO library, so enforce inverted
+	 * semantics.
+	 */
+	par->spi->mode ^= SPI_CS_HIGH;
+	ret = spi_setup(par->spi);
 	if (ret) {
-		dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
+		dev_err(par->info->device,
+			"Could not set inverse CS polarity\n");
 		return ret;
 	}
 	write_reg(par, 0x00); /* make sure mode is set */
-- 
2.23.0

_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

                 reply index

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

Reply instructions:

You may reply publically 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=20191204233230.22309-1-linus.walleij@linaro.org \
    --to=linus.walleij@linaro.org \
    --cc=broonie@kernel.org \
    --cc=devel@driverdev.osuosl.org \
    --cc=gregkh@linuxfoundation.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

DriverDev-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/driverdev-devel/0 driverdev-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 driverdev-devel driverdev-devel/ https://lore.kernel.org/driverdev-devel \
		driverdev-devel@linuxdriverproject.org devel@driverdev.osuosl.org
	public-inbox-index driverdev-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.linuxdriverproject.driverdev-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git