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From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Peter Rosin <peda@axentia.se>
Cc: Wolfram Sang <wsa@the-dreams.de>,
	linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching
Date: Fri, 16 Dec 2016 23:23:56 +0000	[thread overview]
Message-ID: <20161216232355.GO14217@n2100.armlinux.org.uk> (raw)
In-Reply-To: <251c31e3-141c-8884-d56a-fa539714d1ff@axentia.se>

On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
> On 2016-12-16 21:06, Russell King wrote:
> > smbus functions return -ve on error, 0 on success.  However,
> > __i2c_transfer() have a different return signature - -ve on error, or
> > number of buffers transferred (which may be zero or greater.)
> > 
> > The upshot of this is that the sense of the test is reversed when using
> > the mux on a bus supporting the master_xfer method: we cache the value
> > and never retry if we fail to transfer any buffers, but if we succeed,
> > we clear the cached value.
> 
> Ouch! Thanks for catching this.
> 
> > Fix this.
> 
> But lets fix the corner case of __i2c_transfer returning 0 instead of
> the expected 1 as well (not sure if that's even possible, but lets close
> the possibility just in case), so I'd prefer if you could fix
> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
> instead, and -EREMOTEIO on other non-negative return values. Thanks!

So you want something like this instead?

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..9c4ac26c014e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

WARNING: multiple messages have this Message-ID (diff)
From: linux@armlinux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] i2c: mux: pca954x: fix i2c mux selection caching
Date: Fri, 16 Dec 2016 23:23:56 +0000	[thread overview]
Message-ID: <20161216232355.GO14217@n2100.armlinux.org.uk> (raw)
In-Reply-To: <251c31e3-141c-8884-d56a-fa539714d1ff@axentia.se>

On Fri, Dec 16, 2016 at 10:20:35PM +0100, Peter Rosin wrote:
> On 2016-12-16 21:06, Russell King wrote:
> > smbus functions return -ve on error, 0 on success.  However,
> > __i2c_transfer() have a different return signature - -ve on error, or
> > number of buffers transferred (which may be zero or greater.)
> > 
> > The upshot of this is that the sense of the test is reversed when using
> > the mux on a bus supporting the master_xfer method: we cache the value
> > and never retry if we fail to transfer any buffers, but if we succeed,
> > we clear the cached value.
> 
> Ouch! Thanks for catching this.
> 
> > Fix this.
> 
> But lets fix the corner case of __i2c_transfer returning 0 instead of
> the expected 1 as well (not sure if that's even possible, but lets close
> the possibility just in case), so I'd prefer if you could fix
> pca954x_reg_write() to return 0 iff __i2c_transfer(...) returns 1
> instead, and -EREMOTEIO on other non-negative return values. Thanks!

So you want something like this instead?

diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
index 8bc3d36d2837..9c4ac26c014e 100644
--- a/drivers/i2c/muxes/i2c-mux-pca954x.c
+++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
@@ -151,6 +151,9 @@ static int pca954x_reg_write(struct i2c_adapter *adap,
 		buf[0] = val;
 		msg.buf = buf;
 		ret = __i2c_transfer(adap, &msg, 1);
+
+		if (ret >= 0 && ret != 1)
+			ret = -EREMOTEIO;
 	} else {
 		union i2c_smbus_data data;
 		ret = adap->algo->smbus_xfer(adap, client->addr,
@@ -179,7 +182,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret ? 0 : regval;
+		data->last_chan = ret < 0 ? 0 : regval;
 	}
 
 	return ret;


-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently@9.6Mbps down 400kbps up
according to speedtest.net.

  reply	other threads:[~2016-12-16 23:24 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-16 20:06 [PATCH] i2c: mux: pca954x: fix i2c mux selection caching Russell King
2016-12-16 20:06 ` Russell King
2016-12-16 21:20 ` Peter Rosin
2016-12-16 21:20   ` Peter Rosin
2016-12-16 23:23   ` Russell King - ARM Linux [this message]
2016-12-16 23:23     ` Russell King - ARM Linux
2016-12-17  6:50     ` Peter Rosin
2016-12-17  6:50       ` Peter Rosin
2016-12-17 12:10 Russell King
2016-12-17 18:30 ` Wolfram Sang

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