On 30/01/2025 15:34, Kartik Rajput wrote:
> From: Akhil R <akhilrajeev@xxxxxxxxxx>
>
> Add support for SW mutex register introduced in Tegra264 to provide
> an option to share the interface between multiple firmwares and/or
> VMs.
>
> However, the hardware does not ensure any protection based on the
> values. The driver/firmware should honor the peer who already holds
> the mutex.
>
> Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> Signed-off-by: Kartik Rajput <kkartik@xxxxxxxxxx>
> ---
> v1 -> v2:
> * Fixed typos.
> * Fix tegra_i2c_mutex_lock() logic.
> * Add a timeout in tegra_i2c_mutex_lock() instead of polling for
> mutex indefinitely.
> ---
> drivers/i2c/busses/i2c-tegra.c | 132 +++++++++++++++++++++++++++++----
> 1 file changed, 117 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index 7c8b76406e2e..aa92faa6f5cb 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -135,6 +135,14 @@
> #define I2C_MST_FIFO_STATUS_TX GENMASK(23, 16)
> #define I2C_MST_FIFO_STATUS_RX GENMASK(7, 0)
>
> +#define I2C_SW_MUTEX 0x0ec
> +#define I2C_SW_MUTEX_REQUEST GENMASK(3, 0)
> +#define I2C_SW_MUTEX_GRANT GENMASK(7, 4)
> +#define I2C_SW_MUTEX_ID 9
> +
> +/* SW mutex acquire timeout value in milliseconds. */
> +#define I2C_SW_MUTEX_TIMEOUT 25
> +
> /* configuration load timeout in microseconds */
> #define I2C_CONFIG_LOAD_TIMEOUT 1000000
>
> @@ -203,6 +211,7 @@ enum msg_end_type {
> * @has_interface_timing_reg: Has interface timing register to program the tuned
> * timing settings.
> * @has_hs_mode_support: Has support for high speed (HS) mode transfers.
> + * @has_mutex: Has mutex register for mutual exclusion with other firmwares or VM.
> */
> struct tegra_i2c_hw_feature {
> bool has_continue_xfer_support;
> @@ -229,6 +238,7 @@ struct tegra_i2c_hw_feature {
> u32 setup_hold_time_hs_mode;
> bool has_interface_timing_reg;
> bool has_hs_mode_support;
> + bool has_mutex;
> };
>
> /**
> @@ -372,6 +382,103 @@ static void i2c_readsl(struct tegra_i2c_dev *i2c_dev, void *data,
> readsl(i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg), data, len);
> }
>
> +static int tegra_i2c_poll_register(struct tegra_i2c_dev *i2c_dev,
> + u32 reg, u32 mask, u32 delay_us,
> + u32 timeout_us)
> +{
> + void __iomem *addr = i2c_dev->base + tegra_i2c_reg_addr(i2c_dev, reg);
> + u32 val;
> +
> + if (!i2c_dev->atomic_mode)
> + return readl_relaxed_poll_timeout(addr, val, !(val & mask),
> + delay_us, timeout_us);
> +
> + return readl_relaxed_poll_timeout_atomic(addr, val, !(val & mask),
> + delay_us, timeout_us);
> +}
> +
> +static int tegra_i2c_mutex_trylock(struct tegra_i2c_dev *i2c_dev)
> +{
> + u32 val, id;
> +
> + val = i2c_readl(i2c_dev, I2C_SW_MUTEX);
> + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val);
> + if (id != 0 && id != I2C_SW_MUTEX_ID)
> + return 0;
> +
> + val = FIELD_PREP(I2C_SW_MUTEX_REQUEST, I2C_SW_MUTEX_ID);
> + i2c_writel(i2c_dev, val, I2C_SW_MUTEX);
And how do you exactly prevent concurrent, overwriting write? This looks
like pure race.
> +
> + val = i2c_readl(i2c_dev, I2C_SW_MUTEX);
> + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val);
> +
> + if (id != I2C_SW_MUTEX_ID)
> + return 0;
> +
> + return 1;
> +}
> +
> +static void tegra_i2c_mutex_lock(struct tegra_i2c_dev *i2c_dev)
> +{
> + unsigned int num_retries = I2C_SW_MUTEX_TIMEOUT;
> +
> + /* Poll until mutex is acquired or timeout. */
> + while (--num_retries && !tegra_i2c_mutex_trylock(i2c_dev))
> + usleep_range(1000, 2000);
> +
> + WARN_ON(!num_retries);
Blocked thread is not a reason to reboot entire system (see panic on
warn). Drop or change to some dev_warn.
> +}
> +
> +static void tegra_i2c_mutex_unlock(struct tegra_i2c_dev *i2c_dev)
> +{
> + u32 val, id;
> +
> + val = i2c_readl(i2c_dev, I2C_SW_MUTEX);
> + id = FIELD_GET(I2C_SW_MUTEX_GRANT, val);
> +
> + if (WARN_ON(id != I2C_SW_MUTEX_ID))
Same problem here.
Best regards,
Krzysztof
