On Thu, Nov 14, 2019 at 01:47:02PM +0530, shubhrajyoti.datta@xxxxxxxxx wrote:
> From: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>
Typo in the subject.
Run get_maintainers.pl and Cc the right people.
> In case of multimaster configuration the last channel cached value is
> not reliable. Basically the first processor/master does a write to the
> mux and then to the intended slave, it caches the value.
> Now the second processor/processor does a write to mux on another
> channel and writes to another slave.
> The first processor/master when it attempts to write the slave
> skips the mux as it relies on the mux channel being the same as the
> intended. This causes an issue.
>
> To fix that write always to the mux address.
>
> Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt | 1 +
> drivers/i2c/muxes/i2c-mux-pca954x.c | 6 +++++-
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
> index 30ac6a6..fc4c0b0 100644
> --- a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
> @@ -34,6 +34,7 @@ Optional Properties:
> - first cell is the pin number
> - second cell is used to specify flags.
> See also Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
> + - no-channel-cache: Write the mux channel always.
>
> Example:
>
> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
> index 923aa3a..37d32b0 100644
> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> @@ -85,6 +85,7 @@ struct pca954x {
> const struct chip_desc *chip;
>
> u8 last_chan; /* last register value */
> + u8 last_chan_unchached; /* write channel register always */
> /* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
> s8 idle_state;
>
> @@ -244,7 +245,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
> regval = 1 << chan;
>
> /* Only select the channel if its different from the last channel */
> - if (data->last_chan != regval) {
> + if (last_chan_unchached && data->last_chan != regval) {
> ret = pca954x_reg_write(muxc->parent, client, regval);
> data->last_chan = ret < 0 ? 0 : regval;
> }
> @@ -479,6 +480,9 @@ static int pca954x_probe(struct i2c_client *client,
> if (idle_disconnect_dt)
> data->idle_state = MUX_IDLE_DISCONNECT;
>
> + data->last_chan_unchached = np &&
> + of_property_read_bool(np, "no-channel-cache");
> +
> ret = pca954x_irq_setup(muxc);
> if (ret)
> goto fail_cleanup;
> --
> 2.1.1
>
