diff mbox series

[v3,1/3] i2c: use void pointers for supplying data for reads and writes

Message ID 20191112203132.163306-2-dmitry.torokhov@gmail.com
State Rejected
Headers show
Series Use void pointers instead of char in I2C transfer APIs | expand

Commit Message

Dmitry Torokhov Nov. 12, 2019, 8:31 p.m. UTC 
There is no need to force users of i2c_master_send()/i2c_master_recv()
and other i2c read/write bulk data API to cast everything into u8 pointers.
While everything can be considered byte stream, the drivers are usually
work with more structured data.

Let's switch the APIs to accept [const] void pointers to cut amount of
casting needed.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

---

Changes in v3:
- addressed Luca's comments
- added Jonathan's Acked-by

Changes in v2:
- adjusted max1363 to the new i2c_master_send/recv signatures

 drivers/i2c/i2c-core-base.c  |  2 +-
 drivers/i2c/i2c-core-smbus.c | 17 +++++++++--------
 drivers/iio/adc/max1363.c    | 14 ++++++++------
 include/linux/i2c.h          | 28 +++++++++++++++-------------
 4 files changed, 33 insertions(+), 28 deletions(-)

Comments

Luca Ceresoli Nov. 13, 2019, 9:47 a.m. UTC | #1 
Hi Dmitry,

thanks for having taken into account my comments.

On 12/11/19 21:31, Dmitry Torokhov wrote:
> There is no need to force users of i2c_master_send()/i2c_master_recv()
> and other i2c read/write bulk data API to cast everything into u8 pointers.
> While everything can be considered byte stream, the drivers are usually
> work with more structured data.
> 
> Let's switch the APIs to accept [const] void pointers to cut amount of
> casting needed.
> 
> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Uwe Kleine-König Nov. 18, 2019, 7:43 a.m. UTC | #2 
Hello Dmitry,

On Tue, Nov 12, 2019 at 12:31:30PM -0800, Dmitry Torokhov wrote:
> There is no need to force users of i2c_master_send()/i2c_master_recv()
> and other i2c read/write bulk data API to cast everything into u8 pointers.
> While everything can be considered byte stream, the drivers are usually
> work with more structured data.
> 
> Let's switch the APIs to accept [const] void pointers to cut amount of
> casting needed.
> 
> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Can you give an example where you save some casts? Given that i2c is a
byte oriented protocol (as opposed to for example spi) I think it's a
good idea to expose this in the API.

> diff --git a/drivers/iio/adc/max1363.c b/drivers/iio/adc/max1363.c
> index 5c2cc61b666e7..48ed76a0e83d4 100644
> --- a/drivers/iio/adc/max1363.c
> +++ b/drivers/iio/adc/max1363.c

This change isn't motivated in the commit log. Is this here by mistake?

> @@ -182,9 +182,9 @@ struct max1363_state {
>  	struct regulator		*vref;
>  	u32				vref_uv;
>  	int				(*send)(const struct i2c_client *client,
> -						const char *buf, int count);
> +						const void *buf, int count);
>  	int				(*recv)(const struct i2c_client *client,
> -						char *buf, int count);
> +						void *buf, int count);
>  };
>  
>  #define MAX1363_MODE_SINGLE(_num, _mask) {				\
> @@ -310,27 +310,29 @@ static const struct max1363_mode
>  	return NULL;
>  }
>  
> -static int max1363_smbus_send(const struct i2c_client *client, const char *buf,
> +static int max1363_smbus_send(const struct i2c_client *client, const void *buf,
>  		int count)
>  {
> +	const u8 *data = buf;
>  	int i, err;
>  
>  	for (i = err = 0; err == 0 && i < count; ++i)
> -		err = i2c_smbus_write_byte(client, buf[i]);
> +		err = i2c_smbus_write_byte(client, data[i]);

Isn't this hunk an indicator that keeping char (or u8) as type of the
members of buf is a good idea?
 
>  	return err ? err : count;
>  }
>  
> -static int max1363_smbus_recv(const struct i2c_client *client, char *buf,
> +static int max1363_smbus_recv(const struct i2c_client *client, void *buf,
>  		int count)
>  {
> +	u8 *data = buf;
>  	int i, ret;
>  
>  	for (i = 0; i < count; ++i) {
>  		ret = i2c_smbus_read_byte(client);
>  		if (ret < 0)
>  			return ret;
> -		buf[i] = ret;
> +		data[i] = ret;
>  	}
>  
>  	return count;

Best regards
Uwe
Dmitry Torokhov Nov. 18, 2019, 8:04 a.m. UTC | #3 
Hi Uwe,

On Mon, Nov 18, 2019 at 08:43:49AM +0100, Uwe Kleine-König wrote:
> Hello Dmitry,
> 
> On Tue, Nov 12, 2019 at 12:31:30PM -0800, Dmitry Torokhov wrote:
> > There is no need to force users of i2c_master_send()/i2c_master_recv()
> > and other i2c read/write bulk data API to cast everything into u8 pointers.
> > While everything can be considered byte stream, the drivers are usually
> > work with more structured data.
> > 
> > Let's switch the APIs to accept [const] void pointers to cut amount of
> > casting needed.
> > 
> > Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> 
> Can you give an example where you save some casts? Given that i2c is a
> byte oriented protocol (as opposed to for example spi) I think it's a
> good idea to expose this in the API.

I see this at least:

dtor@dtor-ws:~/kernel/work $ git grep "i2c_master.*(u8 \*)"
drivers/crypto/atmel-i2c.c:     ret = i2c_master_send(client, (u8 *)cmd, cmd->count + WORD_ADDR_SIZE);
drivers/iio/common/ms_sensors/ms_sensors_i2c.c:         ret = i2c_master_recv(client, (u8 *)&buf, 3);
drivers/iio/humidity/hdc100x.c: ret = i2c_master_recv(client, (u8 *)buf, 4);
drivers/iio/pressure/abp060mg.c:        ret = i2c_master_send(client, (u8 *)&buf, state->mreq_len);
drivers/iio/pressure/abp060mg.c:        ret = i2c_master_recv(client, (u8 *)&buf, sizeof(buf));
drivers/input/misc/ad714x-i2c.c:        error = i2c_master_send(client, (u8 *)chip->xfer_buf,
drivers/input/misc/ad714x-i2c.c:        error = i2c_master_send(client, (u8 *)chip->xfer_buf,
drivers/input/misc/ad714x-i2c.c:                error = i2c_master_recv(client, (u8 *)chip->xfer_buf,
drivers/input/touchscreen/sx8654.c:     len = i2c_master_recv(ts->client, (u8 *)data, readlen);
drivers/nfc/nfcmrvl/i2c.c:      ret = i2c_master_recv(drv_data->i2c, (u8 *)&nci_hdr, NCI_CTRL_HDR_SIZE);
drivers/nfc/nxp-nci/i2c.c:      r = i2c_master_recv(client, (u8 *) &header, NXP_NCI_FW_HDR_LEN);
drivers/nfc/nxp-nci/i2c.c:      r = i2c_master_recv(client, (u8 *) &header, NCI_CTRL_HDR_SIZE);
drivers/video/fbdev/ssd1307fb.c:        ret = i2c_master_send(client, (u8 *)array, len);

I am pretty sure there are more that my quick grep did not catch.

And I agree that I2C itself is a byte-oriented protocol, but the data from the
point of the driver (once transfer is done) is often more structured.

> 
> > diff --git a/drivers/iio/adc/max1363.c b/drivers/iio/adc/max1363.c
> > index 5c2cc61b666e7..48ed76a0e83d4 100644
> > --- a/drivers/iio/adc/max1363.c
> > +++ b/drivers/iio/adc/max1363.c
> 
> This change isn't motivated in the commit log. Is this here by mistake?

No, it is needed as signature of i2c_master_send/recv has changed.

> 
> > @@ -182,9 +182,9 @@ struct max1363_state {
> >  	struct regulator		*vref;
> >  	u32				vref_uv;
> >  	int				(*send)(const struct i2c_client *client,
> > -						const char *buf, int count);
> > +						const void *buf, int count);
> >  	int				(*recv)(const struct i2c_client *client,
> > -						char *buf, int count);
> > +						void *buf, int count);
> >  };
> >  
> >  #define MAX1363_MODE_SINGLE(_num, _mask) {				\
> > @@ -310,27 +310,29 @@ static const struct max1363_mode
> >  	return NULL;
> >  }
> >  
> > -static int max1363_smbus_send(const struct i2c_client *client, const char *buf,
> > +static int max1363_smbus_send(const struct i2c_client *client, const void *buf,
> >  		int count)
> >  {
> > +	const u8 *data = buf;
> >  	int i, err;
> >  
> >  	for (i = err = 0; err == 0 && i < count; ++i)
> > -		err = i2c_smbus_write_byte(client, buf[i]);
> > +		err = i2c_smbus_write_byte(client, data[i]);
> 
> Isn't this hunk an indicator that keeping char (or u8) as type of the
> members of buf is a good idea?

Not necessarily, if you check the driver sometimes it deals with stream of
bytes, and sometimes it sends structured data, like little-endian words. I
did not make additional changes because I wanted to minimize amount of changes
to this driver in this patch.


>  
> >  	return err ? err : count;
> >  }
> >  
> > -static int max1363_smbus_recv(const struct i2c_client *client, char *buf,
> > +static int max1363_smbus_recv(const struct i2c_client *client, void *buf,
> >  		int count)
> >  {
> > +	u8 *data = buf;
> >  	int i, ret;
> >  
> >  	for (i = 0; i < count; ++i) {
> >  		ret = i2c_smbus_read_byte(client);
> >  		if (ret < 0)
> >  			return ret;
> > -		buf[i] = ret;
> > +		data[i] = ret;
> >  	}
> >  
> >  	return count;
> 

Thanks.
Uwe Kleine-König Nov. 18, 2019, 8:38 a.m. UTC | #4 
[Fixing the address of the linux-iio list]

Hello Dmitry,

On Mon, Nov 18, 2019 at 12:04:46AM -0800, Dmitry Torokhov wrote:
> On Mon, Nov 18, 2019 at 08:43:49AM +0100, Uwe Kleine-König wrote:
> > On Tue, Nov 12, 2019 at 12:31:30PM -0800, Dmitry Torokhov wrote:
> > > There is no need to force users of i2c_master_send()/i2c_master_recv()
> > > and other i2c read/write bulk data API to cast everything into u8 pointers.
> > > While everything can be considered byte stream, the drivers are usually
> > > work with more structured data.
> > > 
> > > Let's switch the APIs to accept [const] void pointers to cut amount of
> > > casting needed.
> > > 
> > > Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> > 
> > Can you give an example where you save some casts? Given that i2c is a
> > byte oriented protocol (as opposed to for example spi) I think it's a
> > good idea to expose this in the API.
> 
> I see this at least:
> 
> dtor@dtor-ws:~/kernel/work $ git grep "i2c_master.*(u8 \*)"
> drivers/crypto/atmel-i2c.c:     ret = i2c_master_send(client, (u8 *)cmd, cmd->count + WORD_ADDR_SIZE);
> drivers/iio/common/ms_sensors/ms_sensors_i2c.c:         ret = i2c_master_recv(client, (u8 *)&buf, 3);
> drivers/iio/humidity/hdc100x.c: ret = i2c_master_recv(client, (u8 *)buf, 4);

I think this one has an endianness bug.

> drivers/iio/pressure/abp060mg.c:        ret = i2c_master_send(client, (u8 *)&buf, state->mreq_len);

From a quick look: mreq_len might be 1 in some cases and buf is declared
as __be16[2]. Hmm.

> drivers/iio/pressure/abp060mg.c:        ret = i2c_master_recv(client, (u8 *)&buf, sizeof(buf));
> drivers/input/misc/ad714x-i2c.c:        error = i2c_master_send(client, (u8 *)chip->xfer_buf,
> drivers/input/misc/ad714x-i2c.c:        error = i2c_master_send(client, (u8 *)chip->xfer_buf,
> drivers/input/misc/ad714x-i2c.c:                error = i2c_master_recv(client, (u8 *)chip->xfer_buf,
> drivers/input/touchscreen/sx8654.c:     len = i2c_master_recv(ts->client, (u8 *)data, readlen);
> drivers/nfc/nfcmrvl/i2c.c:      ret = i2c_master_recv(drv_data->i2c, (u8 *)&nci_hdr, NCI_CTRL_HDR_SIZE);
> drivers/nfc/nxp-nci/i2c.c:      r = i2c_master_recv(client, (u8 *) &header, NXP_NCI_FW_HDR_LEN);
> drivers/nfc/nxp-nci/i2c.c:      r = i2c_master_recv(client, (u8 *) &header, NCI_CTRL_HDR_SIZE);
> drivers/video/fbdev/ssd1307fb.c:        ret = i2c_master_send(client, (u8 *)array, len);
> 
> I am pretty sure there are more that my quick grep did not catch.
> 
> And I agree that I2C itself is a byte-oriented protocol, but the data from the
> point of the driver (once transfer is done) is often more structured.

I think it is fine to require from a caller that they are aware that a
byte (or byte array) must be passed to i2c functions. Given the (maybe)
two problems I pointed out above making it a bit harder to pass non-byte
data to these functions doesn't sound like a bad idea to me.

Obviously your mileage varies, but I personally like having an explicit
type in the API. I guess we have to agree to not agree and let Wolfram
decide if he likes your change or not.

> > > diff --git a/drivers/iio/adc/max1363.c b/drivers/iio/adc/max1363.c
> > > index 5c2cc61b666e7..48ed76a0e83d4 100644
> > > --- a/drivers/iio/adc/max1363.c
> > > +++ b/drivers/iio/adc/max1363.c
> > 
> > This change isn't motivated in the commit log. Is this here by mistake?
> 
> No, it is needed as signature of i2c_master_send/recv has changed.

Ah, I see, there is

	st->send = i2c_master_send;

in the code. I think this is worth mentioning in the commit log that it
changes to this file don't look like a mistake as I wondered.

Best regards
Uwe
Wolfram Sang Jan. 11, 2021, 9:02 p.m. UTC | #5 
> I think it is fine to require from a caller that they are aware that a
> byte (or byte array) must be passed to i2c functions. Given the (maybe)
> two problems I pointed out above making it a bit harder to pass non-byte
> data to these functions doesn't sound like a bad idea to me.
> 
> Obviously your mileage varies, but I personally like having an explicit
> type in the API. I guess we have to agree to not agree and let Wolfram
> decide if he likes your change or not.

I am on Uwe's side here. I like it being explicit and think the casts as
they are now are the smaller problem.
diff mbox series

Patch

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 6a5183cffdfc3..aeb4201ef55e4 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -2065,7 +2065,7 @@  EXPORT_SYMBOL(i2c_transfer);
  *
  * Returns negative errno, or else the number of bytes transferred.
  */
-int i2c_transfer_buffer_flags(const struct i2c_client *client, char *buf,
+int i2c_transfer_buffer_flags(const struct i2c_client *client, void *buf,
 			      int count, u16 flags)
 {
 	int ret;
diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 3ac426a8ab5ab..f8708409b4dbc 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -213,7 +213,7 @@  EXPORT_SYMBOL(i2c_smbus_write_word_data);
  * mechanism (I2C_M_RECV_LEN) which may not be implemented.
  */
 s32 i2c_smbus_read_block_data(const struct i2c_client *client, u8 command,
-			      u8 *values)
+			      void *values)
 {
 	union i2c_smbus_data data;
 	int status;
@@ -240,7 +240,7 @@  EXPORT_SYMBOL(i2c_smbus_read_block_data);
  * else zero on success.
  */
 s32 i2c_smbus_write_block_data(const struct i2c_client *client, u8 command,
-			       u8 length, const u8 *values)
+			       u8 length, const void *values)
 {
 	union i2c_smbus_data data;
 
@@ -256,7 +256,7 @@  EXPORT_SYMBOL(i2c_smbus_write_block_data);
 
 /* Returns the number of read bytes */
 s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client, u8 command,
-				  u8 length, u8 *values)
+				  u8 length, void *values)
 {
 	union i2c_smbus_data data;
 	int status;
@@ -276,7 +276,7 @@  s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client, u8 command,
 EXPORT_SYMBOL(i2c_smbus_read_i2c_block_data);
 
 s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client, u8 command,
-				   u8 length, const u8 *values)
+				   u8 length, const void *values)
 {
 	union i2c_smbus_data data;
 
@@ -628,8 +628,9 @@  EXPORT_SYMBOL(__i2c_smbus_xfer);
  * transfer.
  */
 s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
-					      u8 command, u8 length, u8 *values)
+					      u8 command, u8 length, void *values)
 {
+	u8 *bytes = values;
 	u8 i = 0;
 	int status;
 
@@ -647,8 +648,8 @@  s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
 			status = i2c_smbus_read_word_data(client, command + i);
 			if (status < 0)
 				return status;
-			values[i] = status & 0xff;
-			values[i + 1] = status >> 8;
+			bytes[i] = status & 0xff;
+			bytes[i + 1] = status >> 8;
 			i += 2;
 		}
 	}
@@ -657,7 +658,7 @@  s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
 		status = i2c_smbus_read_byte_data(client, command + i);
 		if (status < 0)
 			return status;
-		values[i] = status;
+		bytes[i] = status;
 		i++;
 	}
 
diff --git a/drivers/iio/adc/max1363.c b/drivers/iio/adc/max1363.c
index 5c2cc61b666e7..48ed76a0e83d4 100644
--- a/drivers/iio/adc/max1363.c
+++ b/drivers/iio/adc/max1363.c
@@ -182,9 +182,9 @@  struct max1363_state {
 	struct regulator		*vref;
 	u32				vref_uv;
 	int				(*send)(const struct i2c_client *client,
-						const char *buf, int count);
+						const void *buf, int count);
 	int				(*recv)(const struct i2c_client *client,
-						char *buf, int count);
+						void *buf, int count);
 };
 
 #define MAX1363_MODE_SINGLE(_num, _mask) {				\
@@ -310,27 +310,29 @@  static const struct max1363_mode
 	return NULL;
 }
 
-static int max1363_smbus_send(const struct i2c_client *client, const char *buf,
+static int max1363_smbus_send(const struct i2c_client *client, const void *buf,
 		int count)
 {
+	const u8 *data = buf;
 	int i, err;
 
 	for (i = err = 0; err == 0 && i < count; ++i)
-		err = i2c_smbus_write_byte(client, buf[i]);
+		err = i2c_smbus_write_byte(client, data[i]);
 
 	return err ? err : count;
 }
 
-static int max1363_smbus_recv(const struct i2c_client *client, char *buf,
+static int max1363_smbus_recv(const struct i2c_client *client, void *buf,
 		int count)
 {
+	u8 *data = buf;
 	int i, ret;
 
 	for (i = 0; i < count; ++i) {
 		ret = i2c_smbus_read_byte(client);
 		if (ret < 0)
 			return ret;
-		buf[i] = ret;
+		data[i] = ret;
 	}
 
 	return count;
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index aaf57d9b41dbb..64cf92e191aa8 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -51,7 +51,7 @@  struct property_entry;
  * @count must be be less than 64k since msg.len is u16.
  */
 extern int i2c_transfer_buffer_flags(const struct i2c_client *client,
-				     char *buf, int count, u16 flags);
+				     void *buf, int count, u16 flags);
 
 /**
  * i2c_master_recv - issue a single I2C message in master receive mode
@@ -62,7 +62,7 @@  extern int i2c_transfer_buffer_flags(const struct i2c_client *client,
  * Returns negative errno, or else the number of bytes read.
  */
 static inline int i2c_master_recv(const struct i2c_client *client,
-				  char *buf, int count)
+				  void *buf, int count)
 {
 	return i2c_transfer_buffer_flags(client, buf, count, I2C_M_RD);
 };
@@ -77,7 +77,7 @@  static inline int i2c_master_recv(const struct i2c_client *client,
  * Returns negative errno, or else the number of bytes read.
  */
 static inline int i2c_master_recv_dmasafe(const struct i2c_client *client,
-					  char *buf, int count)
+					  void *buf, int count)
 {
 	return i2c_transfer_buffer_flags(client, buf, count,
 					 I2C_M_RD | I2C_M_DMA_SAFE);
@@ -92,9 +92,10 @@  static inline int i2c_master_recv_dmasafe(const struct i2c_client *client,
  * Returns negative errno, or else the number of bytes written.
  */
 static inline int i2c_master_send(const struct i2c_client *client,
-				  const char *buf, int count)
+				  const void *buf, int count)
 {
-	return i2c_transfer_buffer_flags(client, (char *)buf, count, 0);
+	return i2c_transfer_buffer_flags(client, (void *)buf /* const cast */,
+					 count, 0);
 };
 
 /**
@@ -107,10 +108,10 @@  static inline int i2c_master_send(const struct i2c_client *client,
  * Returns negative errno, or else the number of bytes written.
  */
 static inline int i2c_master_send_dmasafe(const struct i2c_client *client,
-					  const char *buf, int count)
+					  const void *buf, int count)
 {
-	return i2c_transfer_buffer_flags(client, (char *)buf, count,
-					 I2C_M_DMA_SAFE);
+	return i2c_transfer_buffer_flags(client, (void *)buf /* const cast */,
+					 count, I2C_M_DMA_SAFE);
 };
 
 /* Transfer num messages.
@@ -166,18 +167,19 @@  i2c_smbus_write_word_swapped(const struct i2c_client *client,
 
 /* Returns the number of read bytes */
 extern s32 i2c_smbus_read_block_data(const struct i2c_client *client,
-				     u8 command, u8 *values);
+				     u8 command, void *values);
 extern s32 i2c_smbus_write_block_data(const struct i2c_client *client,
-				      u8 command, u8 length, const u8 *values);
+				      u8 command, u8 length,
+				      const void *values);
 /* Returns the number of read bytes */
 extern s32 i2c_smbus_read_i2c_block_data(const struct i2c_client *client,
-					 u8 command, u8 length, u8 *values);
+					 u8 command, u8 length, void *values);
 extern s32 i2c_smbus_write_i2c_block_data(const struct i2c_client *client,
 					  u8 command, u8 length,
-					  const u8 *values);
+					  const void *values);
 extern s32
 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client *client,
-					  u8 command, u8 length, u8 *values);
+					  u8 command, u8 length, void *values);
 int i2c_get_device_id(const struct i2c_client *client,
 		      struct i2c_device_identity *id);
 #endif /* I2C */