Re: [PATCH v4] Input: mousedev - fix implicit conversion warning

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Nick,

On Mon, May 29, 2017 at 10:41:51PM -0700, Nick Desaulniers wrote:
> Clang warns:
> 
> drivers/input/mousedev.c:653:63: error: implicit conversion from 'int'
> to 'signed char' changes value from 200 to -56
> [-Wconstant-conversion]
>   client->ps2[1] = 0x60; client->ps2[2] = 3; client->ps2[3] = 200;
>                                                             ~ ^~~
> 
> As far as I can tell, from
> 
> http://www.computer-engineering.org/ps2mouse/
> 
> Under "Command Set" > "0xE9 (Status Request)"
> 
> the value 200 is a valid sample rate. Using unsigned char [], rather than
> signed char [], for client->ps2 silences this warning.
> 
> Also moves some reused logic into a helper function.
> 
> Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
> ---
> What's new in v4:
> * replace mousedev_limit_delta() with update_clamped() that also updates
>   the ps2_data and delta values. The use of the temporary val should
>   avoid integral conversion and promotion issues.
> 
>  drivers/input/mousedev.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/input/mousedev.c b/drivers/input/mousedev.c
> index 0e0ff84088fd..e645b8c6f2cb 100644
> --- a/drivers/input/mousedev.c
> +++ b/drivers/input/mousedev.c
> @@ -103,7 +103,7 @@ struct mousedev_client {
>  	spinlock_t packet_lock;
>  	int pos_x, pos_y;
>  
> -	signed char ps2[6];
> +	unsigned char ps2[6];
>  	unsigned char ready, buffer, bufsiz;
>  	unsigned char imexseq, impsseq;
>  	enum mousedev_emul mode;
> @@ -571,27 +571,27 @@ static int mousedev_open(struct inode *inode, struct file *file)
>  	return error;
>  }
>  
> -static inline int mousedev_limit_delta(int delta, int limit)
> +static inline void
> +update_clamped(unsigned char *ps2_data, int *delta, int limit)
>  {
> -	return delta > limit ? limit : (delta < -limit ? -limit : delta);
> +	int val = *delta > limit ? limit : (*delta < -limit ? -limit : *delta);
> +	*ps2_data = (unsigned char) val;
> +	*delta -= val;

Since the time the code was written we got nice helpers to clamp the
values. Does the following work for you or it still leaves clang
unhappy?

Thanks.

-- 
Dmitry


Input: mousedev - fix implicit conversion warning

From: Nick Desaulniers <nick.desaulniers@gmail.com>

Clang warns:

drivers/input/mousedev.c:653:63: error: implicit conversion from 'int'
to 'signed char' changes value from 200 to -56
[-Wconstant-conversion]
  client->ps2[1] = 0x60; client->ps2[2] = 3; client->ps2[3] = 200;
                                                            ~ ^~~
As the PS2 data is really a stream of bytes, let's switch to using u8 type
for it, which silences this warning.

Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
Patchwork-Id: 9753771
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/mousedev.c |   60 +++++++++++++++++++++++++---------------------
 1 file changed, 32 insertions(+), 28 deletions(-)

diff --git a/drivers/input/mousedev.c b/drivers/input/mousedev.c
index 0e0ff84088fd..6ef0c5314f69 100644
--- a/drivers/input/mousedev.c
+++ b/drivers/input/mousedev.c
@@ -15,6 +15,7 @@
 #define MOUSEDEV_MINORS		31
 #define MOUSEDEV_MIX		63
 
+#include <linux/bitops.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/poll.h>
@@ -103,7 +104,7 @@ struct mousedev_client {
 	spinlock_t packet_lock;
 	int pos_x, pos_y;
 
-	signed char ps2[6];
+	u8 ps2[6];
 	unsigned char ready, buffer, bufsiz;
 	unsigned char imexseq, impsseq;
 	enum mousedev_emul mode;
@@ -291,11 +292,10 @@ static void mousedev_notify_readers(struct mousedev *mousedev,
 		}
 
 		client->pos_x += packet->dx;
-		client->pos_x = client->pos_x < 0 ?
-			0 : (client->pos_x >= xres ? xres : client->pos_x);
+		client->pos_x = clamp_val(client->pos_x, 0, xres);
+
 		client->pos_y += packet->dy;
-		client->pos_y = client->pos_y < 0 ?
-			0 : (client->pos_y >= yres ? yres : client->pos_y);
+		client->pos_y = clamp_val(client->pos_y, 0, yres);
 
 		p->dx += packet->dx;
 		p->dy += packet->dy;
@@ -571,44 +571,48 @@ static int mousedev_open(struct inode *inode, struct file *file)
 	return error;
 }
 
-static inline int mousedev_limit_delta(int delta, int limit)
-{
-	return delta > limit ? limit : (delta < -limit ? -limit : delta);
-}
-
-static void mousedev_packet(struct mousedev_client *client,
-			    signed char *ps2_data)
+static void mousedev_packet(struct mousedev_client *client, u8 *ps2_data)
 {
 	struct mousedev_motion *p = &client->packets[client->tail];
+	s8 dx, dy, dz;
+
+	dx = clamp_val(p->dx, -127, 127);
+	p->dx -= dx;
+
+	dy = clamp_val(p->dy, -127, 127);
+	p->dy -= dy;
 
-	ps2_data[0] = 0x08 |
-		((p->dx < 0) << 4) | ((p->dy < 0) << 5) | (p->buttons & 0x07);
-	ps2_data[1] = mousedev_limit_delta(p->dx, 127);
-	ps2_data[2] = mousedev_limit_delta(p->dy, 127);
-	p->dx -= ps2_data[1];
-	p->dy -= ps2_data[2];
+	ps2_data[0] = BIT(3);
+	ps2_data[0] |= ((dx & BIT(7)) >> 3) | ((dy & BIT(7)) >> 2);
+	ps2_data[0] |= p->buttons & 0x07;
 
 	switch (client->mode) {
 	case MOUSEDEV_EMUL_EXPS:
-		ps2_data[3] = mousedev_limit_delta(p->dz, 7);
-		p->dz -= ps2_data[3];
-		ps2_data[3] = (ps2_data[3] & 0x0f) | ((p->buttons & 0x18) << 1);
+		dz = clamp_val(p->dz, -7, 7);
+		p->dz -= dz;
+
+		ps2_data[3] = (dz & 0x0f) | ((p->buttons & 0x18) << 1);
 		client->bufsiz = 4;
 		break;
 
 	case MOUSEDEV_EMUL_IMPS:
-		ps2_data[0] |=
-			((p->buttons & 0x10) >> 3) | ((p->buttons & 0x08) >> 1);
-		ps2_data[3] = mousedev_limit_delta(p->dz, 127);
-		p->dz -= ps2_data[3];
+		dz = clamp_val(p->dz, -127, 127);
+		p->dz -= dz;
+
+		ps2_data[0] |= ((p->buttons & 0x10) >> 3) |
+			       ((p->buttons & 0x08) >> 1);
+		ps2_data[3] = dz;
+
 		client->bufsiz = 4;
 		break;
 
 	case MOUSEDEV_EMUL_PS2:
 	default:
-		ps2_data[0] |=
-			((p->buttons & 0x10) >> 3) | ((p->buttons & 0x08) >> 1);
 		p->dz = 0;
+
+		ps2_data[0] |= ((p->buttons & 0x10) >> 3) |
+                               ((p->buttons & 0x08) >> 1);
+
 		client->bufsiz = 3;
 		break;
 	}
@@ -714,7 +718,7 @@ static ssize_t mousedev_read(struct file *file, char __user *buffer,
 {
 	struct mousedev_client *client = file->private_data;
 	struct mousedev *mousedev = client->mousedev;
-	signed char data[sizeof(client->ps2)];
+	u8 data[sizeof(client->ps2)];
 	int retval = 0;
 
 	if (!client->ready && !client->buffer && mousedev->exist &&