diff mbox

[v5,02/23] drm/i2c: tda998x: check more I/O errors

Message ID 9ebf1fdd613b5747aefb3ee21c9c246d102f1a47.1390986082.git.moinejf@free.fr (mailing list archive)
State New, archived
Headers show

Commit Message

Jean-Francois Moine Jan. 25, 2014, 5:14 p.m. UTC 
This patch adds more error checking inn I2C I/O functions.
In case of I/O error, this permits to avoid writing in bad controller
pages, a bad chipset detection or looping when getting the EDID.

Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
---
 drivers/gpu/drm/i2c/tda998x_drv.c | 57 +++++++++++++++++++++++++++++----------
 1 file changed, 43 insertions(+), 14 deletions(-)

Comments

Russell King - ARM Linux Feb. 2, 2014, 4:20 p.m. UTC | #1 
On Sat, Jan 25, 2014 at 06:14:45PM +0100, Jean-Francois Moine wrote:
> This patch adds more error checking inn I2C I/O functions.
> In case of I/O error, this permits to avoid writing in bad controller
> pages, a bad chipset detection or looping when getting the EDID.

I've just looked at this again, and spotted something:

> -static uint8_t
> +static int
>  reg_read(struct tda998x_priv *priv, uint16_t reg)
>  {
>  	uint8_t val = 0;
> -	reg_read_range(priv, reg, &val, sizeof(val));
> +	int ret;
> +
> +	ret = reg_read_range(priv, reg, &val, sizeof(val));
> +	if (ret < 0)
> +		return ret;

So yes, this can return negative numbers.

> @@ -1158,8 +1184,11 @@ tda998x_encoder_init(struct i2c_client *client,
>  	tda998x_reset(priv);
>  
>  	/* read version: */
> -	priv->rev = reg_read(priv, REG_VERSION_LSB) |
> -			reg_read(priv, REG_VERSION_MSB) << 8;
> +	ret = reg_read(priv, REG_VERSION_LSB) |
> +		(reg_read(priv, REG_VERSION_MSB) << 8);
> +	if (ret < 0)
> +		goto fail;
> +	priv->rev = ret;

Two issues here:

1. The additional parens are /really/ not required.
2. What if reg_read(priv, REG_VERSION_MSB) returns a negative number?

If we're going to the extent of attempting to make the read/write
functions return errors, we should at least handle errors generated
by them properly, otherwise it's pointless making them return errors.

	ret = reg_read(priv, REG_VERSION_LSB);
	if (ret < 0)
		goto fail;

	priv->rev = ret;

	ret = reg_read(priv, REG_VERSION_MSB);
	if (ret < 0)
		goto fail;

	priv->rev |= ret << 8;

If you want it to look slightly nicer:

	int rev_lo, rev_hi;

	rev_lo = reg_read(priv, REG_VERSION_LSB);
	rev_hi = reg_read(priv, REG_VERSION_MSB);
	if (rev_lo < 0 || rev_hi < 0) {
		ret = rev_lo < 0 ? rev_lo : rev_hi;
		goto fail;
	}

	priv->rev = rev_lo | rev_hi << 8;

I'm happy to commit such a change after this patch to clean it up, or if
you want to regenerate your patch 2 and post /just/ that incorporating
this change.
Jean-Francois Moine Feb. 2, 2014, 5:30 p.m. UTC | #2 
On Sun, 2 Feb 2014 16:20:58 +0000
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> On Sat, Jan 25, 2014 at 06:14:45PM +0100, Jean-Francois Moine wrote:
> > This patch adds more error checking inn I2C I/O functions.
> > In case of I/O error, this permits to avoid writing in bad controller
> > pages, a bad chipset detection or looping when getting the EDID.
> 
> I've just looked at this again, and spotted something:
> 
> > -static uint8_t
> > +static int
> >  reg_read(struct tda998x_priv *priv, uint16_t reg)
> >  {
> >  	uint8_t val = 0;
> > -	reg_read_range(priv, reg, &val, sizeof(val));
> > +	int ret;
> > +
> > +	ret = reg_read_range(priv, reg, &val, sizeof(val));
> > +	if (ret < 0)
> > +		return ret;
> 
> So yes, this can return negative numbers.
> 
> > @@ -1158,8 +1184,11 @@ tda998x_encoder_init(struct i2c_client *client,
> >  	tda998x_reset(priv);
> >  
> >  	/* read version: */
> > -	priv->rev = reg_read(priv, REG_VERSION_LSB) |
> > -			reg_read(priv, REG_VERSION_MSB) << 8;
> > +	ret = reg_read(priv, REG_VERSION_LSB) |
> > +		(reg_read(priv, REG_VERSION_MSB) << 8);
> > +	if (ret < 0)
> > +		goto fail;
> > +	priv->rev = ret;
> 
> Two issues here:
> 
> 1. The additional parens are /really/ not required.
> 2. What if reg_read(priv, REG_VERSION_MSB) returns a negative number?
> 
> If we're going to the extent of attempting to make the read/write
> functions return errors, we should at least handle errors generated
> by them properly, otherwise it's pointless making them return errors.
> 
> 	ret = reg_read(priv, REG_VERSION_LSB);
> 	if (ret < 0)
> 		goto fail;
> 
> 	priv->rev = ret;
> 
> 	ret = reg_read(priv, REG_VERSION_MSB);
> 	if (ret < 0)
> 		goto fail;
> 
> 	priv->rev |= ret << 8;
> 
> If you want it to look slightly nicer:
> 
> 	int rev_lo, rev_hi;
> 
> 	rev_lo = reg_read(priv, REG_VERSION_LSB);
> 	rev_hi = reg_read(priv, REG_VERSION_MSB);
> 	if (rev_lo < 0 || rev_hi < 0) {
> 		ret = rev_lo < 0 ? rev_lo : rev_hi;
> 		goto fail;
> 	}
> 
> 	priv->rev = rev_lo | rev_hi << 8;
> 
> I'm happy to commit such a change after this patch to clean it up, or if
> you want to regenerate your patch 2 and post /just/ that incorporating
> this change.

I think that my code works correctly: when there is an error, the
result of reg_read() is minus the error code, and this error code is
always lower than 8388607 (0x7fffff). Then, reg_read() << 8 will always
be negative.

Otherwise, I may redo a patch about the useless parenthesis.
Russell King - ARM Linux Feb. 2, 2014, 5:56 p.m. UTC | #3 
On Sun, Feb 02, 2014 at 06:30:00PM +0100, Jean-Francois Moine wrote:
> On Sun, 2 Feb 2014 16:20:58 +0000
> Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
> 
> > On Sat, Jan 25, 2014 at 06:14:45PM +0100, Jean-Francois Moine wrote:
> > > This patch adds more error checking inn I2C I/O functions.
> > > In case of I/O error, this permits to avoid writing in bad controller
> > > pages, a bad chipset detection or looping when getting the EDID.
> > 
> > I've just looked at this again, and spotted something:
> > 
> > > -static uint8_t
> > > +static int
> > >  reg_read(struct tda998x_priv *priv, uint16_t reg)
> > >  {
> > >  	uint8_t val = 0;
> > > -	reg_read_range(priv, reg, &val, sizeof(val));
> > > +	int ret;
> > > +
> > > +	ret = reg_read_range(priv, reg, &val, sizeof(val));
> > > +	if (ret < 0)
> > > +		return ret;
> > 
> > So yes, this can return negative numbers.
> > 
> > > @@ -1158,8 +1184,11 @@ tda998x_encoder_init(struct i2c_client *client,
> > >  	tda998x_reset(priv);
> > >  
> > >  	/* read version: */
> > > -	priv->rev = reg_read(priv, REG_VERSION_LSB) |
> > > -			reg_read(priv, REG_VERSION_MSB) << 8;
> > > +	ret = reg_read(priv, REG_VERSION_LSB) |
> > > +		(reg_read(priv, REG_VERSION_MSB) << 8);
> > > +	if (ret < 0)
> > > +		goto fail;
> > > +	priv->rev = ret;
> > 
> > Two issues here:
> > 
> > 1. The additional parens are /really/ not required.
> > 2. What if reg_read(priv, REG_VERSION_MSB) returns a negative number?
> > 
> > If we're going to the extent of attempting to make the read/write
> > functions return errors, we should at least handle errors generated
> > by them properly, otherwise it's pointless making them return errors.
> > 
> > 	ret = reg_read(priv, REG_VERSION_LSB);
> > 	if (ret < 0)
> > 		goto fail;
> > 
> > 	priv->rev = ret;
> > 
> > 	ret = reg_read(priv, REG_VERSION_MSB);
> > 	if (ret < 0)
> > 		goto fail;
> > 
> > 	priv->rev |= ret << 8;
> > 
> > If you want it to look slightly nicer:
> > 
> > 	int rev_lo, rev_hi;
> > 
> > 	rev_lo = reg_read(priv, REG_VERSION_LSB);
> > 	rev_hi = reg_read(priv, REG_VERSION_MSB);
> > 	if (rev_lo < 0 || rev_hi < 0) {
> > 		ret = rev_lo < 0 ? rev_lo : rev_hi;
> > 		goto fail;
> > 	}
> > 
> > 	priv->rev = rev_lo | rev_hi << 8;
> > 
> > I'm happy to commit such a change after this patch to clean it up, or if
> > you want to regenerate your patch 2 and post /just/ that incorporating
> > this change.
> 
> I think that my code works correctly: when there is an error, the
> result of reg_read() is minus the error code, and this error code is
> always lower than 8388607 (0x7fffff). Then, reg_read() << 8 will always
> be negative.

The issue I'm pointing out is not whether it will be interpreted as an
error or not, it's whether the value is a correct error code.  If we
don't care about the reason why an error occurs, we might as well just
return -1.

I've added my own patch which adjusts it as per above to my tree anyway,
so I'm not that worried about this.
diff mbox

Patch

diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
index 26dd299..11f0607 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -362,7 +362,7 @@  fail:
 	return 0;
 }
 
-static void
+static int
 set_page(struct tda998x_priv *priv, uint16_t reg)
 {
 	if (REG2PAGE(reg) != priv->current_page) {
@@ -371,11 +371,14 @@  set_page(struct tda998x_priv *priv, uint16_t reg)
 				REG_CURPAGE, REG2PAGE(reg)
 		};
 		int ret = i2c_master_send(client, buf, sizeof(buf));
-		if (ret < 0)
+		if (ret < 0) {
 			dev_err(&client->dev, "Error %d writing to REG_CURPAGE\n", ret);
+			return ret;
+		}
 
 		priv->current_page = REG2PAGE(reg);
 	}
+	return 0;
 }
 
 static int
@@ -385,7 +388,9 @@  reg_read_range(struct tda998x_priv *priv, uint16_t reg, char *buf, int cnt)
 	uint8_t addr = REG2ADDR(reg);
 	int ret;
 
-	set_page(priv, reg);
+	ret = set_page(priv, reg);
+	if (ret < 0)
+		return ret;
 
 	ret = i2c_master_send(client, &addr, sizeof(addr));
 	if (ret < 0)
@@ -412,18 +417,24 @@  reg_write_range(struct tda998x_priv *priv, uint16_t reg, uint8_t *p, int cnt)
 	buf[0] = REG2ADDR(reg);
 	memcpy(&buf[1], p, cnt);
 
-	set_page(priv, reg);
+	ret = set_page(priv, reg);
+	if (ret < 0)
+		return;
 
 	ret = i2c_master_send(client, buf, cnt + 1);
 	if (ret < 0)
 		dev_err(&client->dev, "Error %d writing to 0x%x\n", ret, reg);
 }
 
-static uint8_t
+static int
 reg_read(struct tda998x_priv *priv, uint16_t reg)
 {
 	uint8_t val = 0;
-	reg_read_range(priv, reg, &val, sizeof(val));
+	int ret;
+
+	ret = reg_read_range(priv, reg, &val, sizeof(val));
+	if (ret < 0)
+		return ret;
 	return val;
 }
 
@@ -434,7 +445,9 @@  reg_write(struct tda998x_priv *priv, uint16_t reg, uint8_t val)
 	uint8_t buf[] = {REG2ADDR(reg), val};
 	int ret;
 
-	set_page(priv, reg);
+	ret = set_page(priv, reg);
+	if (ret < 0)
+		return;
 
 	ret = i2c_master_send(client, buf, ARRAY_SIZE(buf));
 	if (ret < 0)
@@ -448,7 +461,9 @@  reg_write16(struct tda998x_priv *priv, uint16_t reg, uint16_t val)
 	uint8_t buf[] = {REG2ADDR(reg), val >> 8, val};
 	int ret;
 
-	set_page(priv, reg);
+	ret = set_page(priv, reg);
+	if (ret < 0)
+		return;
 
 	ret = i2c_master_send(client, buf, ARRAY_SIZE(buf));
 	if (ret < 0)
@@ -458,13 +473,21 @@  reg_write16(struct tda998x_priv *priv, uint16_t reg, uint16_t val)
 static void
 reg_set(struct tda998x_priv *priv, uint16_t reg, uint8_t val)
 {
-	reg_write(priv, reg, reg_read(priv, reg) | val);
+	int old_val;
+
+	old_val = reg_read(priv, reg);
+	if (old_val >= 0)
+		reg_write(priv, reg, old_val | val);
 }
 
 static void
 reg_clear(struct tda998x_priv *priv, uint16_t reg, uint8_t val)
 {
-	reg_write(priv, reg, reg_read(priv, reg) & ~val);
+	int old_val;
+
+	old_val = reg_read(priv, reg);
+	if (old_val >= 0)
+		reg_write(priv, reg, old_val & ~val);
 }
 
 static void
@@ -970,8 +993,10 @@  read_edid_block(struct drm_encoder *encoder, uint8_t *buf, int blk)
 
 	/* wait for block read to complete: */
 	for (i = 100; i > 0; i--) {
-		uint8_t val = reg_read(priv, REG_INT_FLAGS_2);
-		if (val & INT_FLAGS_2_EDID_BLK_RD)
+		ret = reg_read(priv, REG_INT_FLAGS_2);
+		if (ret < 0)
+			return ret;
+		if (ret & INT_FLAGS_2_EDID_BLK_RD)
 			break;
 		msleep(1);
 	}
@@ -1134,6 +1159,7 @@  tda998x_encoder_init(struct i2c_client *client,
 		    struct drm_encoder_slave *encoder_slave)
 {
 	struct tda998x_priv *priv;
+	int ret;
 
 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	if (!priv)
@@ -1158,8 +1184,11 @@  tda998x_encoder_init(struct i2c_client *client,
 	tda998x_reset(priv);
 
 	/* read version: */
-	priv->rev = reg_read(priv, REG_VERSION_LSB) |
-			reg_read(priv, REG_VERSION_MSB) << 8;
+	ret = reg_read(priv, REG_VERSION_LSB) |
+		(reg_read(priv, REG_VERSION_MSB) << 8);
+	if (ret < 0)
+		goto fail;
+	priv->rev = ret;
 
 	/* mask off feature bits: */
 	priv->rev &= ~0x30; /* not-hdcp and not-scalar bit */