diff mbox

[2/13] drivers/media/tuners/mxl5007t.c: use macros for i2c_msg initialization

Message ID 1349624323-15584-4-git-send-email-Julia.Lawall@lip6.fr (mailing list archive)
State New, archived
Headers show

Commit Message

Julia Lawall Oct. 7, 2012, 3:38 p.m. UTC 
From: Julia Lawall <Julia.Lawall@lip6.fr>

Introduce use of I2c_MSG_READ/WRITE/OP, for readability.

In each case, a length expressed as an explicit constant is also
re-expressed as the size of the buffer, when this is possible.

A simplified version of the semantic patch that makes this change is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression a,b,c;
identifier x;
@@

struct i2c_msg x =
- {.addr = a, .buf = b, .len = c, .flags = I2C_M_RD}
+ I2C_MSG_READ(a,b,c)
 ;

@@
expression a,b,c;
identifier x;
@@

struct i2c_msg x =
- {.addr = a, .buf = b, .len = c, .flags = 0}
+ I2C_MSG_WRITE(a,b,c)
 ;

@@
expression a,b,c,d;
identifier x;
@@

struct i2c_msg x = 
- {.addr = a, .buf = b, .len = c, .flags = d}
+ I2C_MSG_OP(a,b,c,d)
 ;
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>

---
 drivers/media/tuners/mxl5007t.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)


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Comments

Jean Delvare Oct. 9, 2012, 12:30 p.m. UTC | #1 
Hi Julia,

On Sun,  7 Oct 2012 17:38:33 +0200, Julia Lawall wrote:
> From: Julia Lawall <Julia.Lawall@lip6.fr>
> 
> Introduce use of I2c_MSG_READ/WRITE/OP, for readability.

Next time you send this patch set, please Cc me on every post so that I
don't have to hunt for them on lkml.org.

> In each case, a length expressed as an explicit constant is also
> re-expressed as the size of the buffer, when this is possible.

This is conceptually wrong, please don't do that. It is perfectly valid
to use a buffer which is larger than the message being written or read.
When exchanging multiple messages, it is actually quite common to
declare only 2 buffers and reuse them:

	char reg;
	char val[2];

	struct i2c_msg msg[2] = {
		{ .addr = addr, .flags = 0, .buf = &reg, .len = 1 },
		{ .addr = addr, .flags = I2C_M_RD, .buf = val, .len = 1 },
	};

	reg = 0x04;
	i2c_transfer(i2c_adap, msg, 2);
	/* Do stuff with val */

	reg = 0x06;
	msg[1].len = 2;
	i2c_transfer(i2c_adap, msg, 2);
	/* Do stuff with val */

Your conversion would read 2 bytes from register 0x04 instead of 1 in
the example above.

I am not opposed to the idea of i2c_msg initialization helper macros,
but please don't mix that with actual code changes which could have bad
side effects.

Thanks,
Julia Lawall Oct. 9, 2012, 12:50 p.m. UTC | #2 
On Tue, 9 Oct 2012, Jean Delvare wrote:

> Hi Julia,
>
> On Sun,  7 Oct 2012 17:38:33 +0200, Julia Lawall wrote:
> > From: Julia Lawall <Julia.Lawall@lip6.fr>
> >
> > Introduce use of I2c_MSG_READ/WRITE/OP, for readability.
>
> Next time you send this patch set, please Cc me on every post so that I
> don't have to hunt for them on lkml.org.

OK.

> > In each case, a length expressed as an explicit constant is also
> > re-expressed as the size of the buffer, when this is possible.
>
> This is conceptually wrong, please don't do that. It is perfectly valid
> to use a buffer which is larger than the message being written or read.
> When exchanging multiple messages, it is actually quite common to
> declare only 2 buffers and reuse them:
>
> 	char reg;
> 	char val[2];
>
> 	struct i2c_msg msg[2] = {
> 		{ .addr = addr, .flags = 0, .buf = &reg, .len = 1 },
> 		{ .addr = addr, .flags = I2C_M_RD, .buf = val, .len = 1 },
> 	};
>
> 	reg = 0x04;
> 	i2c_transfer(i2c_adap, msg, 2);
> 	/* Do stuff with val */
>
> 	reg = 0x06;
> 	msg[1].len = 2;
> 	i2c_transfer(i2c_adap, msg, 2);
> 	/* Do stuff with val */
>
> Your conversion would read 2 bytes from register 0x04 instead of 1 in
> the example above.
>
> I am not opposed to the idea of i2c_msg initialization helper macros,
> but please don't mix that with actual code changes which could have bad
> side effects.

I at least tried to check in every case that the result of sizeof is the
same as the value that is present.  But I can leave the constants as is,
if that seems better.

Thanks for the feedback.

julia
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diff mbox

Patch

diff --git a/drivers/media/tuners/mxl5007t.c b/drivers/media/tuners/mxl5007t.c
index 69e453e..c0c28be 100644
--- a/drivers/media/tuners/mxl5007t.c
+++ b/drivers/media/tuners/mxl5007t.c
@@ -464,8 +464,8 @@  reg_pair_t *mxl5007t_calc_rf_tune_regs(struct mxl5007t_state *state,
 static int mxl5007t_write_reg(struct mxl5007t_state *state, u8 reg, u8 val)
 {
 	u8 buf[] = { reg, val };
-	struct i2c_msg msg = { .addr = state->i2c_props.addr, .flags = 0,
-			       .buf = buf, .len = 2 };
+	struct i2c_msg msg = I2C_MSG_WRITE(state->i2c_props.addr, buf,
+					   sizeof(buf));
 	int ret;
 
 	ret = i2c_transfer(state->i2c_props.adap, &msg, 1);
@@ -494,10 +494,8 @@  static int mxl5007t_read_reg(struct mxl5007t_state *state, u8 reg, u8 *val)
 {
 	u8 buf[2] = { 0xfb, reg };
 	struct i2c_msg msg[] = {
-		{ .addr = state->i2c_props.addr, .flags = 0,
-		  .buf = buf, .len = 2 },
-		{ .addr = state->i2c_props.addr, .flags = I2C_M_RD,
-		  .buf = val, .len = 1 },
+		I2C_MSG_WRITE(state->i2c_props.addr, buf, sizeof(buf)),
+		I2C_MSG_READ(state->i2c_props.addr, val, 1),
 	};
 	int ret;
 
@@ -512,10 +510,8 @@  static int mxl5007t_read_reg(struct mxl5007t_state *state, u8 reg, u8 *val)
 static int mxl5007t_soft_reset(struct mxl5007t_state *state)
 {
 	u8 d = 0xff;
-	struct i2c_msg msg = {
-		.addr = state->i2c_props.addr, .flags = 0,
-		.buf = &d, .len = 1
-	};
+	struct i2c_msg msg = I2C_MSG_WRITE(state->i2c_props.addr, &d,
+					   sizeof(d));
 	int ret = i2c_transfer(state->i2c_props.adap, &msg, 1);
 
 	if (ret != 1) {