linux-kernel - Re: [PATCH 2.6.28] mfd: Correct WM8350 I2C return code usage

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Date:	Thu, 13 Nov 2008 00:06:36 +0100
From:	Samuel Ortiz <sameo@...nedhand.com>
To:	Mark Brown <broonie@...ena.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.28] mfd: Correct WM8350 I2C return code usage

On Wed, Nov 12, 2008 at 08:00:07PM +0000, Mark Brown wrote:
> On Wed, Nov 12, 2008 at 07:49:57PM +0100, Samuel Ortiz wrote:
> > On Mon, Nov 10, 2008 at 01:41:17PM +0000, Mark Brown wrote:
> 
> > > The vendor BSP used for the WM8350 development provided an I2C driver
> > > which incorrectly returned zero on succesful sends rather than the
> > > number of transmitted bytes, an error which was then propagated into the
> > > WM8350 I2C accessors.
> 
> > Shouldnt we fix the accessors behaviour instead ?
> > Currently, that would mean fixing some of the wm8350-core static functions.
> > Slightly bigger patch, but that would keep the i2c interface consistent.
> 
> I don't really understand what you mean by "keep the i2c interface
> consistent" here?  The purpose of this abstraction is to abstract away
> the control interface used to communicate with the chip since it
> supports both I2C and SPI.
I understand that. I'm just saying that I would prefer wm8350->read_dev() to
return the actual bytes read, be it for SPI or I2C. Same for write_dev(), of
course.
With this patch you're breaking that expectation because the read|write_dev()
callers basically expect it to return 0 when the you've read|written the right
number of bytes.
I'd prefer to fix the callers code, so that we keep the expected semantics
for your read|write_dev() routines. For example with wm8350_clear_bits():

diff --git a/drivers/mfd/wm8350-core.c b/drivers/mfd/wm8350-core.c
index 0d47fb9..12ff3a6 100644
--- a/drivers/mfd/wm8350-core.c
+++ b/drivers/mfd/wm8350-core.c
@@ -199,19 +199,22 @@ static int wm8350_write(struct wm8350 *wm8350, u8 reg, int num_regs, u16 *src)
 int wm8350_clear_bits(struct wm8350 *wm8350, u16 reg, u16 mask)
 {
 	u16 data;
-	int err;
+	int err = 0, ret;
 
 	mutex_lock(&io_mutex);
-	err = wm8350_read(wm8350, reg, 1, &data);
-	if (err) {
+	ret = wm8350_read(wm8350, reg, 1, &data);
+	if (ret != 1) {
 		dev_err(wm8350->dev, "read from reg R%d failed\n", reg);
+		err = -EIO;
 		goto out;
 	}
 
 	data &= ~mask;
-	err = wm8350_write(wm8350, reg, 1, &data);
-	if (err)
+	ret = wm8350_write(wm8350, reg, 1, &data);
+	if (ret != 1) {
 		dev_err(wm8350->dev, "write to reg R%d failed\n", reg);
+		err = -EIO;
+	}
 out:
 	mutex_unlock(&io_mutex);
 	return err;


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