On 12/15/2016 04:11 PM, Phil Reid wrote:

On 15/12/2016 20:33, Andy Shevchenko wrote:

quoted

On Thu, 2016-12-15 at 16:59 +0800, Zhangfei Gao wrote:

quoted

Some platforms like hi3660 need do reset first to allow accessing
registers

Patch itself looks good, but would be nice to have it tested.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

quoted

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
---
 drivers/i2c/busses/i2c-designware-core.h    |  1 +
 drivers/i2c/busses/i2c-designware-platdrv.c | 28
++++++++++++++++++++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-core.h

b/drivers/i2c/busses/i2c-designware-core.h
index 0d44d2a..94b14fa 100644

--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h

@@ -80,6 +80,7 @@ struct dw_i2c_dev {
     void __iomem        *base;
     struct completion    cmd_complete;
     struct clk        *clk;
+    struct reset_control    *rst;
     u32            (*get_clk_rate_khz) (struct

dw_i2c_dev *dev);
     struct dw_pci_controller *controller;
     int            cmd_err;

diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c

b/drivers/i2c/busses/i2c-designware-platdrv.c
index 0b42a12..e9016ae 100644

--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c

@@ -38,6 +38,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/property.h>
 #include <linux/io.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 #include <linux/acpi.h>
 #include <linux/platform_data/i2c-designware.h>

@@ -176,6 +177,14 @@ static int dw_i2c_plat_probe(struct

platform_device *pdev)
     dev->irq = irq;
     platform_set_drvdata(pdev, dev);

+    dev->rst = devm_reset_control_get_optional(&pdev->dev, NULL);
+    if (IS_ERR(dev->rst)) {
+        if (PTR_ERR(dev->rst) == -EPROBE_DEFER)
+            return -EPROBE_DEFER;
+    } else {
+        reset_control_deassert(dev->rst);
+    }
+

More for my education. But some drivers seem to handle the error codes a
little more explicitly.
Whats the best approach?

eg: From usb/dwc2 driver it continues only if ENOENT / ENOTSUPP errors
are return
and ENOMEM / EINVAL etc is a fatal error.

hsotg->reset = devm_reset_control_get_optional(hsotg->dev, "dwc2");
if (IS_ERR(hsotg->reset)) {
        ret = PTR_ERR(hsotg->reset);
        switch (ret) {
        case -ENOENT:
        case -ENOTSUPP:
                hsotg->reset = NULL;
                break;
        default:
                dev_err(hsotg->dev, "error getting reset control %d\n",
                        ret);
                return ret;
        }

This looks a bit extreme. At least we shouldn't spam log on machines 
that don't need reset control. I kind of think it's good enough to do 
like the patch does. I.e. handle only EPROBE_DEFER and let all other 
errors fall through and keep the controller in reset and let the 
dev->rst carry an error code.

I guess EINVAL is likely seen by developer only. ENOMEM is so fatal that 
things are already falling apart somewhere else too and I don't think it 
needs special handling here.

-- 
Jarkko