[PATCH] i2c: s3c2410: Add SMBus emulation for block read

[PATCH] i2c: s3c2410: Add SMBus emulation for block read

[Prasanna Kumar]

From: Jaemin Yoo <jmin.yoo-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>

SMBus read and write are supported by the emulation layer of i2c
framework if the controller doesn't have SMBus features.

I2C_M_RECV_LEN flag is used to let i2c drivers know rx length is not
yet determined but will be read to the first byte in rx buffer.

s3c2410 doesn't handle this flag. So only one byte is read from slave.
There fore following two features are added to the driver code.

1. skip rx length check if I2C_M_RECV_LEN is set and the length is 1.
2. add actual bytes to the rx length after reading first bytes if
   I2C_M_RECV_LEN.

I2C_M_RECV_LEN is only set for SMBus command. So this code does not
affect legacy codes which only use i2c command for s3c2410.

Signed-off-by: Jaemin Yoo <jmin.yoo-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
Tested-by: Prasanna Kumar <prasanna.ps-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
---
 drivers/i2c/busses/i2c-s3c2410.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c
index 17c5c37..e4ab9ea 100644
--- a/drivers/i2c/busses/i2c-s3c2410.c
+++ b/drivers/i2c/busses/i2c-s3c2410.c
@@ -309,6 +309,12 @@ static inline int is_lastmsg(struct s3c24xx_i2c *i2c)
 
 static inline int is_msglast(struct s3c24xx_i2c *i2c)
 {
+	/* msg->len is always 1 for the first byte of smbus block read.
+	 * Actual length will be read from slave. More bytes will be
+	 * read according to the length then. */
+	if (i2c->msg->flags & I2C_M_RECV_LEN && i2c->msg->len == 1)
+		return 0;
+
 	return i2c->msg_ptr == i2c->msg->len-1;
 }
 
@@ -448,6 +454,9 @@ static int i2c_s3c_irq_nextbyte(struct s3c24xx_i2c *i2c, unsigned long iicstat)
 		byte = readb(i2c->regs + S3C2410_IICDS);
 		i2c->msg->buf[i2c->msg_ptr++] = byte;
 
+		/* Add actual length to read for smbus block read */
+		if (i2c->msg->flags & I2C_M_RECV_LEN && i2c->msg->len == 1)
+			i2c->msg->len += byte;
  prepare_read:
 		if (is_msglast(i2c)) {
 			/* last byte of buffer */
-- 
1.7.10.4

Re: [PATCH] i2c: s3c2410: Add SMBus emulation for block read

[Wolfram Sang]

On Tue, Mar 26, 2013 at 07:59:56PM +0530, Prasanna Kumar wrote:
> From: Jaemin Yoo <jmin.yoo-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
> 
> SMBus read and write are supported by the emulation layer of i2c
> framework if the controller doesn't have SMBus features.
> 
> I2C_M_RECV_LEN flag is used to let i2c drivers know rx length is not
> yet determined but will be read to the first byte in rx buffer.
> 
> s3c2410 doesn't handle this flag. So only one byte is read from slave.
> There fore following two features are added to the driver code.
> 
> 1. skip rx length check if I2C_M_RECV_LEN is set and the length is 1.
> 2. add actual bytes to the rx length after reading first bytes if
>    I2C_M_RECV_LEN.
> 
> I2C_M_RECV_LEN is only set for SMBus command. So this code does not
> affect legacy codes which only use i2c command for s3c2410.
> 
> Signed-off-by: Jaemin Yoo <jmin.yoo-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
> Tested-by: Prasanna Kumar <prasanna.ps-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>

Applied to for-next, thanks!

Re: [PATCH] i2c: s3c2410: Add SMBus emulation for block read

[Uwe Kleine-König]

Hello,

On Tue, Mar 26, 2013 at 07:59:56PM +0530, Prasanna Kumar wrote:
> diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c
> index 17c5c37..e4ab9ea 100644
> --- a/drivers/i2c/busses/i2c-s3c2410.c
> +++ b/drivers/i2c/busses/i2c-s3c2410.c
> @@ -309,6 +309,12 @@ static inline int is_lastmsg(struct s3c24xx_i2c *i2c)
>  
>  static inline int is_msglast(struct s3c24xx_i2c *i2c)
>  {
> +	/* msg->len is always 1 for the first byte of smbus block read.
> +	 * Actual length will be read from slave. More bytes will be
> +	 * read according to the length then. */
> +	if (i2c->msg->flags & I2C_M_RECV_LEN && i2c->msg->len == 1)
> +		return 0;
> +
>  	return i2c->msg_ptr == i2c->msg->len-1;
>  }
>  
> @@ -448,6 +454,9 @@ static int i2c_s3c_irq_nextbyte(struct s3c24xx_i2c *i2c, unsigned long iicstat)
>  		byte = readb(i2c->regs + S3C2410_IICDS);
>  		i2c->msg->buf[i2c->msg_ptr++] = byte;
>  
> +		/* Add actual length to read for smbus block read */
> +		if (i2c->msg->flags & I2C_M_RECV_LEN && i2c->msg->len == 1)
> +			i2c->msg->len += byte;
>   prepare_read:
>  		if (is_msglast(i2c)) {
I don't know if that can happen, but if the block has length 0 (that is,
only consists of a single byte that is read as 0) the is_msglast() test
returns 0 which might be wrong. Maybe even if it cannot regularily
happen handle it in a sane way?

Also I wonder if error checking for byte > I2C_SMBUS_BLOCK_MAX would be
needed to prevent a buffer overrun?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [PATCH] i2c: s3c2410: Add SMBus emulation for block read

[Wolfram Sang]

> I don't know if that can happen, but if the block has length 0 (that is,
> only consists of a single byte that is read as 0) the is_msglast() test
> returns 0 which might be wrong. Maybe even if it cannot regularily
> happen handle it in a sane way?

Length of 0 is illegal according to the specs, but a check won't hurt.

> Also I wonder if error checking for byte > I2C_SMBUS_BLOCK_MAX would be
> needed to prevent a buffer overrun?

Yes. Although I have seen devices able to send more than that, yet
adding support for that is a seperate issue.