linux-kernel - [PATCH 1/4] spi: Add parameter for clock to rx delay

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Message-Id: <20231026152316.2729575-2-estl@gmx.net>
Date:   Thu, 26 Oct 2023 17:23:02 +0200
From:   Eberhard Stoll <estl@....net>
To:     linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
        Mark Brown <broonie@...nel.org>
Cc:     Eberhard Stoll <eberhard.stoll@...tron.de>,
        Frieder Schrempf <frieder.schrempf@...tron.de>,
        Amit Kumar Mahapatra <amit.kumar-mahapatra@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Leonard Göhrs <l.goehrs@...gutronix.de>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: [PATCH 1/4] spi: Add parameter for clock to rx delay

From: Eberhard Stoll <eberhard.stoll@...tron.de>

For spi devices the master clock output defines the sampling point
for receive data input stream (rising or falling edge). The receive
data stream from the device is delayed in relation to the master
clock output.

For some devices this delay is larger than one half clock period,
which is normally the sampling point for receive data. In this case
receive data is sampled too early and the device fails to operate.
In consequence the spi clock has to be reduced to match the delay
characteristics and this reduces performance and is therefore not
recommended.

Some spi controllers implement a 'clock to receive data delay'
compensation which shifts the receive sampling point. So we need
a property to set this value for each spi device.

Add a parameter 'rx_sample_delay_ns' to enable setting the clock
to rx data delay for each spi device separately.

The 'clock to receive data delay' value is often referenced as tCLQV
in spi device data sheets.

Signed-off-by: Eberhard Stoll <eberhard.stoll@...tron.de>
Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
---
 include/linux/spi/spi.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 7f8b478fdeb3..14622d47f44f 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -166,6 +166,7 @@ extern void spi_transfer_cs_change_delay_exec(struct spi_message *msg,
  * @cs_inactive: delay to be introduced by the controller after CS is
  *	deasserted. If @cs_change_delay is used from @spi_transfer, then the
  *	two delays will be added up.
+ * @rx_sample_delay_ns: spi clk to spi rx data delay
  * @pcpu_statistics: statistics for the spi_device
  *
  * A @spi_device is used to interchange data between an SPI slave
@@ -219,6 +220,8 @@ struct spi_device {
 	struct spi_delay	cs_setup;
 	struct spi_delay	cs_hold;
 	struct spi_delay	cs_inactive;
+	/* Transfer characteristics */
+	u32			rx_sample_delay_ns; /* Clock to RX data delay */

 	/* The statistics */
 	struct spi_statistics __percpu	*pcpu_statistics;
--
2.25.1