From: Matheus Tavares <matheus.bernardino@usp.br>
To: Lars-Peter Clausen <lars@metafoo.de>,
Michael Hennerich <Michael.Hennerich@analog.com>,
Jonathan Cameron <jic23@kernel.org>,
Hartmut Knaack <knaack.h@gmx.de>,
Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>
Cc: linux-iio@vger.kernel.org, devel@driverdev.osuosl.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
Alexandru Ardelean <alexandru.ardelean@analog.com>,
kernel-usp@googlegroups.com, victorcolombo@gmail.com
Subject: [PATCH v2 3/7] staging:iio:ad2s90: Add max frequency check at probe
Date: Sun, 18 Nov 2018 02:25:36 -0200 [thread overview]
Message-ID: <20181118042540.12697-4-matheus.bernardino@usp.br> (raw)
In-Reply-To: <20181118042540.12697-1-matheus.bernardino@usp.br>
From: Alexandru Ardelean <alexandru.ardelean@analog.com>
This patch adds a max frequency check at the beginning of ad2s90_probe
function so that when it is set to a value above 0.83Mhz, dev_err is
called with an appropriate message and -EINVAL is returned.
The defined limit is 0.83Mhz instead of 2Mhz, which is the chip's max
frequency as specified in the datasheet, because, as also specified in
the datasheet, a 600ns delay is expected between the application of a
logic LO to CS and the application of SCLK. Since the delay is not
implemented in the spi code, to satisfy it, SCLK's period should be at
most 2 * 600ns, so the max frequency should be 1 / (2 * 6e-7), which
gives roughly 830000Hz.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
---
Changes in v2:
- Correctly credit Alexandru as the patch's author
drivers/staging/iio/resolver/ad2s90.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/staging/iio/resolver/ad2s90.c b/drivers/staging/iio/resolver/ad2s90.c
index 913d6fad2d4d..fe90f2056bff 100644
--- a/drivers/staging/iio/resolver/ad2s90.c
+++ b/drivers/staging/iio/resolver/ad2s90.c
@@ -19,6 +19,12 @@
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
+/*
+ * Although chip's max frequency is 2Mhz, it needs 600ns between CS and the
+ * first falling edge of SCLK, so frequency should be at most 1 / (2 * 6e-7)
+ */
+#define AD2S90_MAX_SPI_FREQ_HZ 830000
+
struct ad2s90_state {
struct mutex lock;
struct spi_device *sdev;
@@ -78,6 +84,12 @@ static int ad2s90_probe(struct spi_device *spi)
struct iio_dev *indio_dev;
struct ad2s90_state *st;
+ if (spi->max_speed_hz > AD2S90_MAX_SPI_FREQ_HZ) {
+ dev_err(&spi->dev, "SPI CLK, %d Hz exceeds %d Hz\n",
+ spi->max_speed_hz, AD2S90_MAX_SPI_FREQ_HZ);
+ return -EINVAL;
+ }
+
indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
if (!indio_dev)
return -ENOMEM;
--
2.18.0
next prev parent reply other threads:[~2018-11-18 4:26 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-18 4:25 [PATCH v2 0/7] staging:iio:ad2s90: Add dt support and move out of staging Matheus Tavares
2018-11-18 4:25 ` [PATCH v2 1/7] staging:iio:ad2s90: Add device tree support Matheus Tavares
2018-11-19 8:09 ` Ardelean, Alexandru
2018-11-20 23:59 ` Matheus Tavares Bernardino
2018-11-21 19:12 ` Jonathan Cameron
2018-11-18 4:25 ` [PATCH v2 2/7] staging:iio:ad2s90: Remove spi setup that should be done via dt Matheus Tavares
2018-11-18 4:25 ` Matheus Tavares [this message]
2018-11-19 8:18 ` [PATCH v2 3/7] staging:iio:ad2s90: Add max frequency check at probe Ardelean, Alexandru
2018-11-18 4:25 ` [PATCH v2 4/7] dt-bindings:iio:resolver: Add docs for ad2s90 Matheus Tavares
2018-11-19 8:22 ` Ardelean, Alexandru
2018-11-20 23:34 ` Matheus Tavares Bernardino
2018-11-18 4:25 ` [PATCH v2 5/7] staging:iio:ad2s90: Replace license text w/ SPDX identifier Matheus Tavares
2018-11-18 4:25 ` [PATCH v2 6/7] staging:iio:ad2s90: Add comment to device state mutex Matheus Tavares
2018-11-18 4:25 ` [PATCH v2 7/7] staging:iio:ad2s90: Move out of staging Matheus Tavares
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