linux-kernel - Re: [PATCH 3/3] i2c: mux: pca9541: prepare for PCA9641 support

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Date:   Wed, 21 Mar 2018 01:17:39 +0200
From:   Vladimir Zapolskiy <vz@...ia.com>
To:     Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org,
        Ken Chen <chen.kenyy@...entec.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Wolfram Sang <wsa@...-dreams.de>, joel@....id.au,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH 3/3] i2c: mux: pca9541: prepare for PCA9641 support

Hi Peter, Ken,

On 03/20/2018 11:32 AM, Peter Rosin wrote:
> Make the arbitrate and release_bus implementation chip specific.
> 

by chance I took a look at the original implementation done by Ken, and
I would say that this 3/3 change is an overkill as a too generic one.
Is there any next observable extension? And do two abstracted (*arbitrate)
and (*release_bus) cover it well? Probably no.

At first it would be simpler to add a new chip id field into struct pca9541
(struct rename would be needed of course), and do a selection of specific
pca9x41_arbitrate() and pca9x41_release_bus() depending on it:

----8<----
diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c
index 47685eb..a40e6d8 100644
--- a/drivers/i2c/muxes/i2c-mux-pca9541.c
+++ b/drivers/i2c/muxes/i2c-mux-pca9541.c
@@ -70,8 +70,13 @@
 #define SELECT_DELAY_SHORT	50
 #define SELECT_DELAY_LONG	1000
 
+enum chip_id {
+	pca9541,
+};
+
 struct pca9541 {
 	struct i2c_client *client;
+	enum chip_id id;
 	unsigned long select_timeout;
 	unsigned long arb_timeout;
 };
@@ -188,10 +193,13 @@ static int pca9541_reg_read(struct i2c_client *client, u8 command)
  */
 
 /* Release bus. Also reset NTESTON and BUSINIT if it was set. */
-static void pca9541_release_bus(struct i2c_client *client)
+static void pca9541_release_bus(struct i2c_client *client, enum chip_id id)
 {
 	int reg;
 
+	if (id != pca9541)
+		return;
+
 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
 	if (reg >= 0 && !pca9541_busoff(reg) && pca9541_mybus(reg))
 		pca9541_reg_write(client, PCA9541_CONTROL,
@@ -235,12 +243,15 @@ static const u8 pca9541_control[16] = {
  *  0 : bus not acquired
  *  1 : bus acquired
  */
-static int pca9541_arbitrate(struct i2c_client *client)
+static int pca9541_arbitrate(struct i2c_client *client, enum chip_id id)
 {
 	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
 	struct pca9541 *data = i2c_mux_priv(muxc);
 	int reg;
 
+	if (id != pca9541)
+		return -EOPNOTSUPP;
+
 	reg = pca9541_reg_read(client, PCA9541_CONTROL);
 	if (reg < 0)
 		return reg;
@@ -318,7 +329,7 @@ static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
 		/* force bus ownership after this time */
 
 	do {
-		ret = pca9541_arbitrate(client);
+		ret = pca9541_arbitrate(client, data->id);
 		if (ret)
 			return ret < 0 ? ret : 0;
 
@@ -336,7 +347,7 @@ static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
 	struct pca9541 *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
 
-	pca9541_release_bus(client);
+	pca9541_release_bus(client, data->id);
 	return 0;
 }
 
@@ -361,7 +372,7 @@ static int pca9541_probe(struct i2c_client *client,
 	 * We have to lock the adapter before releasing the bus.
 	 */
 	i2c_lock_adapter(adap);
-	pca9541_release_bus(client);
+	pca9541_release_bus(client, pca9541);
 	i2c_unlock_adapter(adap);
 
 	/* Create mux adapter */
@@ -377,6 +388,7 @@ static int pca9541_probe(struct i2c_client *client,
 
 	data = i2c_mux_priv(muxc);
 	data->client = client;
+	data->id = pca9541;
 
 	i2c_set_clientdata(client, muxc);
 
----8<----


> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  drivers/i2c/muxes/i2c-mux-pca9541.c | 62 +++++++++++++++++++++++++++----------
>  1 file changed, 45 insertions(+), 17 deletions(-)
> 

The change above is trivial and it does not cancel any further
extensions similar to your idea, the open question is if there
is a demand right at the moment.

> diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c
> index 47685eb4e0e9..cac629e36bf8 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca9541.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca9541.c
> @@ -23,6 +23,7 @@
>  #include <linux/i2c-mux.h>
>  #include <linux/jiffies.h>
>  #include <linux/module.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_data/pca954x.h>
>  #include <linux/slab.h>
>  
> @@ -70,26 +71,22 @@
>  #define SELECT_DELAY_SHORT	50
>  #define SELECT_DELAY_LONG	1000
>  
> -struct pca9541 {
> -	struct i2c_client *client;
> -	unsigned long select_timeout;
> -	unsigned long arb_timeout;
> +enum chip_name {

chip_name sound like a string storage, chip_id might be better here.

> +	pca9541,
>  };
>  

--
With best wishes,
Vladimir