drm/xe/i2c: Keep the i2c controller always enabled

Some platforms make an assumption that the i2c controller's
enabled state indicates also the power state of the
controller. This can create a problem when the controller is
in disabled state, because the hardware may assume
incorrectly that it is then also in low-power state.

To fix this, the controller is kept enabled by taking over
the IC_ENABLE register. The controller has to be disabled
when the configuration is updated and when the target
address or the slave address are assigned, so disabling it
when IC_CON, IC_TAR or IC_SAR registers are programmed, and
then re-enabling it again.

Fixes: f0e53aadd702 ("drm/xe: Support for I2C attached MCUs")
Cc: stable@vger.kernel.org
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patch.msgid.link/20260811121008.1493015-4-heikki.krogerus@linux.intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
(cherry picked from commit 76cc14e2faed1adae20f4ee144ead0e3a7566c49)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_i2c.c b/drivers/gpu/drm/xe/xe_i2c.c
index 32767570e43d4af3aa47d6049449251d7e19c84b..d8fa68206f418fe2cf56eaced35736382b787895 100644 (file)
--- a/drivers/gpu/drm/xe/xe_i2c.c
+++ b/drivers/gpu/drm/xe/xe_i2c.c
@@ -8,6 +8,7 @@
 #include <drm/drm_print.h>
 #include <linux/array_size.h>
 #include <linux/container_of.h>
+#include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
@@ -215,11 +216,40 @@ void xe_i2c_irq_postinstall(struct xe_device *xe)
        xe_mmio_rmw32(mmio, I2C_CONFIG_CMD, PCI_COMMAND_INTX_DISABLE, 0);
 }
 
+/* See "Disabling DW_apb_i2c" in the DesignWare DW_abp_i2c databook. */
+static void xe_i2c_disable(struct xe_i2c *i2c)
+{
+       int timeout = 100;
+       u32 status;
+
+       xe_mmio_rmw32(i2c->mmio, I2C_REG(DW_IC_ENABLE), DW_IC_ENABLE_ENABLE, 0);
+
+       do {
+               status = xe_mmio_read32(i2c->mmio, I2C_REG(DW_IC_ENABLE_STATUS));
+               if (!(status & DW_IC_ENABLE_ENABLE))
+                       return;
+               /* Can't sleep here. */
+               udelay(25);
+       } while (timeout--);
+
+       dev_warn(i2c->drm_dev, "timeout in disabling i2c adapter\n");
+}
+
 static int xe_i2c_read(void *context, unsigned int reg, unsigned int *val)
 {
        struct xe_i2c *i2c = context;
 
-       *val = xe_mmio_read32(i2c->mmio, XE_REG(reg + I2C_MEM_SPACE_OFFSET));
+       *val = xe_mmio_read32(i2c->mmio, I2C_REG(reg));
+
+       switch (reg) {
+       case DW_IC_ENABLE:
+       case DW_IC_ENABLE_STATUS:
+               FIELD_MODIFY(DW_IC_ENABLE_ENABLE, val,
+                            i2c->ic_enable & DW_IC_ENABLE_ENABLE);
+               break;
+       default:
+               break;
+       }
 
        return 0;
 }
@@ -229,6 +259,23 @@ static int xe_i2c_write(void *context, unsigned int reg, unsigned int val)
        struct xe_i2c *i2c = context;
 
        switch (reg) {
+       case DW_IC_CON:
+       case DW_IC_TAR:
+       case DW_IC_SAR:
+               /* Disable the controller. */
+               xe_i2c_disable(i2c);
+
+               /* Write the register. */
+               xe_mmio_write32(i2c->mmio, I2C_REG(reg), val);
+
+               /* Enable the controller. */
+               xe_mmio_rmw32(i2c->mmio, I2C_REG(DW_IC_ENABLE), 0, DW_IC_ENABLE_ENABLE);
+               return 0;
+       case DW_IC_ENABLE:
+               i2c->ic_enable = val;
+               /* Other fields can be updated except the enable bit. */
+               val |= DW_IC_ENABLE_ENABLE;
+               break;
        case DW_IC_SMBUS_INTR_MASK:
                /* Make sure the Alert is never masked. */
                val |= DW_IC_SMBUS_INTR_ALERT;

diff --git a/drivers/gpu/drm/xe/xe_i2c.h b/drivers/gpu/drm/xe/xe_i2c.h
index b200966b0048493654694cd2c79b85dd14b98a6f..d63adacfefe71b3ae695987f104f978959a7e2c5 100644 (file)
--- a/drivers/gpu/drm/xe/xe_i2c.h
+++ b/drivers/gpu/drm/xe/xe_i2c.h
@@ -37,6 +37,7 @@ struct xe_i2c {
        struct platform_device *pdev;
        struct i2c_adapter *adapter;
        struct i2c_client *client[XE_I2C_MAX_CLIENTS];
+       unsigned int ic_enable;
 
        struct notifier_block bus_notifier;
        struct work_struct work;