linux-kernel - [PATCH] i2c: at91: ensure state is restored after suspending

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Message-Id: <20170130172533.31995-1-alexandre.belloni@free-electrons.com>
Date:   Mon, 30 Jan 2017 18:25:33 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     Ludovic Desroches <ludovic.desroches@...el.com>,
        linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: [PATCH] i2c: at91: ensure state is restored after suspending

When going to suspend, the I2C registers may be lost because the power to
VDDcore is cut. Save them and restore them when resuming.

Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
---
 drivers/i2c/busses/i2c-at91.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index 0b86c6173e07..633bdd899952 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -140,6 +140,12 @@ struct at91_twi_dev {
 	unsigned transfer_status;
 	struct i2c_adapter adapter;
 	unsigned twi_cwgr_reg;
+	struct {
+		u32 mmr;
+		u32 imr;
+		u32 fmr;
+		u32 fimr;
+	} cache;
 	struct at91_twi_pdata *pdata;
 	bool use_dma;
 	bool use_alt_cmd;
@@ -1172,6 +1178,15 @@ static int at91_twi_runtime_resume(struct device *dev)
 
 static int at91_twi_suspend_noirq(struct device *dev)
 {
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
+
+	twi_dev->cache.mmr = at91_twi_read(twi_dev, AT91_TWI_MMR);
+	twi_dev->cache.imr = at91_twi_read(twi_dev, AT91_TWI_IMR);
+	if (twi_dev->fifo_size) {
+		twi_dev->cache.fmr = at91_twi_read(twi_dev, AT91_TWI_FMR);
+		twi_dev->cache.fimr = at91_twi_read(twi_dev, AT91_TWI_FIMR);
+	}
+
 	if (!pm_runtime_status_suspended(dev))
 		at91_twi_runtime_suspend(dev);
 
@@ -1180,6 +1195,7 @@ static int at91_twi_suspend_noirq(struct device *dev)
 
 static int at91_twi_resume_noirq(struct device *dev)
 {
+	struct at91_twi_dev *twi_dev = dev_get_drvdata(dev);
 	int ret;
 
 	if (!pm_runtime_status_suspended(dev)) {
@@ -1191,6 +1207,14 @@ static int at91_twi_resume_noirq(struct device *dev)
 	pm_runtime_mark_last_busy(dev);
 	pm_request_autosuspend(dev);
 
+	at91_init_twi_bus(twi_dev);
+	at91_twi_write(twi_dev, AT91_TWI_MMR, twi_dev->cache.mmr);
+	at91_twi_write(twi_dev, AT91_TWI_IER, twi_dev->cache.imr);
+	if (twi_dev->fifo_size) {
+		at91_twi_write(twi_dev, AT91_TWI_FMR, twi_dev->cache.fmr);
+		at91_twi_write(twi_dev, AT91_TWI_FIER, twi_dev->cache.fimr);
+	}
+
 	return 0;
 }
 
-- 
2.11.0