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SubjectRe: [PATCH v2 1/3] i3c: fix i2c and i3c scl rate by bus mode
On Thu,  6 Jun 2019 16:00:01 +0200
Vitor Soares <Vitor.Soares@synopsys.com> wrote:

> Currently the I3C framework limits SCL frequency to FM speed when
> dealing with a mixed slow bus, even if all I2C devices are FM+ capable.
>
> The core was also not accounting for I3C speed limitations when
> operating in mixed slow mode and was erroneously using FM+ speed as the
> max I2C speed when operating in mixed fast mode.
>
> Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> Signed-off-by: Vitor Soares <vitor.soares@synopsys.com>
> Cc: Boris Brezillon <bbrezillon@kernel.org>
> Cc: <stable@vger.kernel.org>
> Cc: <linux-kernel@vger.kernel.org>
> ---
> Changes in v2:
> Enhance commit message
> Add dev_warn() in case user-defined i2c rate doesn't match LVR constraint
> Add dev_warn() in case user-defined i3c rate lower than i2c rate.
>
> drivers/i3c/master.c | 61 +++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 48 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index 5f4bd52..8cd5824 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -91,6 +91,12 @@ void i3c_bus_normaluse_unlock(struct i3c_bus *bus)
> up_read(&bus->lock);
> }
>
> +static struct i3c_master_controller *
> +i3c_bus_to_i3c_master(struct i3c_bus *i3cbus)
> +{
> + return container_of(i3cbus, struct i3c_master_controller, bus);
> +}
> +
> static struct i3c_master_controller *dev_to_i3cmaster(struct device *dev)
> {
> return container_of(dev, struct i3c_master_controller, dev);
> @@ -565,20 +571,48 @@ static const struct device_type i3c_masterdev_type = {
> .groups = i3c_masterdev_groups,
> };
>
> -int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode)
> +int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
> + unsigned long max_i2c_scl_rate)
> {
> - i3cbus->mode = mode;
>
> - if (!i3cbus->scl_rate.i3c)
> - i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> + struct i3c_master_controller *master = i3c_bus_to_i3c_master(i3cbus);
>
> - if (!i3cbus->scl_rate.i2c) {
> - if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW)
> - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> - else
> - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> + i3cbus->mode = mode;
> +
> + switch (i3cbus->mode) {
> + case I3C_BUS_MODE_PURE:
> + if (!i3cbus->scl_rate.i3c)
> + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> + break;
> + case I3C_BUS_MODE_MIXED_FAST:
> + if (!i3cbus->scl_rate.i3c)
> + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> + if (!i3cbus->scl_rate.i2c)
> + i3cbus->scl_rate.i2c = max_i2c_scl_rate;
> + break;
> + case I3C_BUS_MODE_MIXED_SLOW:
> + if (!i3cbus->scl_rate.i2c)
> + i3cbus->scl_rate.i2c = max_i2c_scl_rate;
> + if (!i3cbus->scl_rate.i3c ||
> + i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> + i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> + break;
> + default:
> + return -EINVAL;
> }
>
> + if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
> + dev_warn(&master->dev,
> + "i3c-scl-hz=%ld lower than i2c-scl-hz=%ld\n",
> + i3cbus->scl_rate.i3c, i3cbus->scl_rate.i2c);
> +
> + if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE &&
> + i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_PLUS_SCL_RATE &&
> + i3cbus->mode != I3C_BUS_MODE_PURE)

If you are so strict, there's clearly no point exposing an i2c-scl-hz
property. I'm still not convinced having an i2c rate that's slower than
what the I2C/I3C spec defines as the *typical* rate is a bad thing, just
like I'm not convinced having an I3C rate that's slower than the I2C
one is a problem (it's definitely a weird situation, but there's nothing
preventing that in the spec).

> + dev_warn(&master->dev,
> + "i2c-scl-hz=%ld not defined according MIPI I3C spec\n"
> + , i3cbus->scl_rate.i2c);

The comma should be on the previous line.

> +
> /*
> * I3C/I2C frequency may have been overridden, check that user-provided
> * values are not exceeding max possible frequency.
> @@ -1966,9 +2000,6 @@ of_i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
> /* LVR is encoded in reg[2]. */
> boardinfo->lvr = reg[2];
>
> - if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
> - master->bus.scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> -
> list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
> of_node_get(node);
>
> @@ -2417,6 +2448,7 @@ int i3c_master_register(struct i3c_master_controller *master,
> const struct i3c_master_controller_ops *ops,
> bool secondary)
> {
> + unsigned long i2c_scl_rate = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> struct i3c_bus *i3cbus = i3c_master_get_bus(master);
> enum i3c_bus_mode mode = I3C_BUS_MODE_PURE;
> struct i2c_dev_boardinfo *i2cbi;
> @@ -2466,9 +2498,12 @@ int i3c_master_register(struct i3c_master_controller *master,
> ret = -EINVAL;
> goto err_put_dev;
> }
> +
> + if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
> + i2c_scl_rate = I3C_BUS_I2C_FM_SCL_RATE;
> }
>
> - ret = i3c_bus_set_mode(i3cbus, mode);
> + ret = i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
> if (ret)
> goto err_put_dev;
>

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