Re: [PATCH 2/3] i3c: master: Extend address status bit to 4 and add I3C_ADDR_SLOT_EXT_INIT

[Miquel Raynal]

Hi Frank,

Frank.Li@xxxxxxx wrote on Tue, 01 Oct 2024 13:08:21 -0400:

> Extend the address status bit to 4 and introduce the I3C_ADDR_SLOT_EXT_INIT
> macro to indicate that a device prefers a specific address. This is
> generally set by the 'assigned-address' in the device tree source (dts)
> file.
> 
>  ┌────┬─────────────┬───┬─────────┬───┐
>  │S/Sr│ 7'h7E RnW=0 │ACK│ ENTDAA  │ T ├────┐
>  └────┴─────────────┴───┴─────────┴───┘    │
>  ┌─────────────────────────────────────────┘
>  │  ┌──┬─────────────┬───┬─────────────────┬────────────────┬───┬─────────┐
>  └─►│Sr│7'h7E RnW=1  │ACK│48bit UID BCR DCR│Assign 7bit Addr│PAR│ ACK/NACK│
>     └──┴─────────────┴───┴─────────────────┴────────────────┴───┴─────────┘
> 
> Some master controllers (such as HCI) need to prepare the entire above
> transaction before sending it out to the I3C bus. This means that a 7-bit
> dynamic address needs to be allocated before knowing the target device's
> UID information.
> 
> However, some I3C targets want a specific address (called as
> "init_dyn_addr"), which is typically specified by the DT's assigned-address
> property. (Lower addresses have higher IBI priority, and the target can
> adjust this by using the assigned-address property if using DT). The
> function i3c_master_add_i3c_dev_locked() will switch to this
> "init_dyn_addr" if it is not in use.
> 
> Therefore, i3c_bus_get_free_addr() should return a free address that has
> not been claimed by any target devices as "init_dyn_addr" (indicated by
> I3C_ADDR_SLOT_EXT_INIT). This allows the device with the "init_dyn_addr"
> to switch to its "init_dyn_addr" when it hot-joins the I3C bus. Otherwise,
> if the "init_dyn_addr" is already in use by another I3C device, the target
> device will not be able to switch to its desired address.
> 
> If all of above address are already used, i3c_bus_get_free_addr() return
> one from the claimed as init_dyn_addr and free address slot. This ensures
> support devices as much as possible.
> 
> Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> ---
> change from v3 to v4
> - rewrite commit message and comment for i3c_bus_get_free_addr()
> ---
>  drivers/i3c/master.c       | 68 ++++++++++++++++++++++++++++++++++++++++------
>  include/linux/i3c/master.h |  7 +++--
>  2 files changed, 64 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> index dcf8d23c5941a..a56cb281e6b6d 100644
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c
> @@ -345,7 +345,7 @@ const struct bus_type i3c_bus_type = {
>  EXPORT_SYMBOL_GPL(i3c_bus_type);
>  
>  static enum i3c_addr_slot_status
> -i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
> +i3c_bus_get_addr_slot_status_ext(struct i3c_bus *bus, u16 addr)
>  {
>  	unsigned long status;
>  	int bitpos = addr * I3C_ADDR_SLOT_STATUS_BITS;
> @@ -356,11 +356,17 @@ i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
>  	status = bus->addrslots[bitpos / BITS_PER_LONG];
>  	status >>= bitpos % BITS_PER_LONG;
>  
> -	return status & I3C_ADDR_SLOT_STATUS_MASK;
> +	return status & I3C_ADDR_SLOT_EXT_STATUS_MASK;
>  }
>  
> -static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
> -					 enum i3c_addr_slot_status status)
> +static enum i3c_addr_slot_status
> +i3c_bus_get_addr_slot_status(struct i3c_bus *bus, u16 addr)
> +{
> +	return i3c_bus_get_addr_slot_status_ext(bus, addr) & I3C_ADDR_SLOT_STATUS_MASK;
> +}
> +
> +static void i3c_bus_set_addr_slot_status_mask(struct i3c_bus *bus, u16 addr,
> +					      enum i3c_addr_slot_status status, int mask)
>  {
>  	int bitpos = addr * I3C_ADDR_SLOT_STATUS_BITS;
>  	unsigned long *ptr;
> @@ -369,11 +375,22 @@ static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
>  		return;
>  
>  	ptr = bus->addrslots + (bitpos / BITS_PER_LONG);
> -	*ptr &= ~((unsigned long)I3C_ADDR_SLOT_STATUS_MASK <<
> -						(bitpos % BITS_PER_LONG));
> +	*ptr &= ~((unsigned long)mask << (bitpos % BITS_PER_LONG));
>  	*ptr |= (unsigned long)status << (bitpos % BITS_PER_LONG);
>  }
>  
> +static void i3c_bus_set_addr_slot_status(struct i3c_bus *bus, u16 addr,
> +					 enum i3c_addr_slot_status status)
> +{
> +	i3c_bus_set_addr_slot_status_mask(bus, addr, status, I3C_ADDR_SLOT_STATUS_MASK);
> +}
> +
> +static void i3c_bus_set_addr_slot_status_ext(struct i3c_bus *bus, u16 addr,
> +					     enum i3c_addr_slot_status status)
> +{
> +	i3c_bus_set_addr_slot_status_mask(bus, addr, status, I3C_ADDR_SLOT_EXT_STATUS_MASK);
> +}

Can we drop this helper and instead modify the
i3c_bus_set_addr_slot_status() prototype to get the mask from its
parameters? 

> +
>  static bool i3c_bus_dev_addr_is_avail(struct i3c_bus *bus, u8 addr)
>  {
>  	enum i3c_addr_slot_status status;
> @@ -383,11 +400,44 @@ static bool i3c_bus_dev_addr_is_avail(struct i3c_bus *bus, u8 addr)
>  	return status == I3C_ADDR_SLOT_FREE;
>  }
>  
> +/*
> + * ┌────┬─────────────┬───┬─────────┬───┐
> + * │S/Sr│ 7'h7E RnW=0 │ACK│ ENTDAA  │ T ├────┐
> + * └────┴─────────────┴───┴─────────┴───┘    │
> + * ┌─────────────────────────────────────────┘
> + * │  ┌──┬─────────────┬───┬─────────────────┬────────────────┬───┬─────────┐
> + * └─►│Sr│7'h7E RnW=1  │ACK│48bit UID BCR DCR│Assign 7bit Addr│PAR│ ACK/NACK│
> + *    └──┴─────────────┴───┴─────────────────┴────────────────┴───┴─────────┘
> + * Some master controllers (such as HCI) need to prepare the entire above transaction before
> + * sending it out to the I3C bus. This means that a 7-bit dynamic address needs to be allocated
> + * before knowing the target device's UID information.
> + *
> + * However, some I3C targets want a specific address (called as "init_dyn_addr"), which is

				may request specific addresses (called "init...

> + * typically specified by the DT's assigned-address property. (Lower addresses have higher IBI

				   -'s

> + * priority, and the target can adjust this by using the assigned-address property if using DT).

Can we remove the whole "( ... )" sentence, and replace it with:

	"... property, lower addresses having higher IBI priority."

> + * The function i3c_master_add_i3c_dev_locked() will switch to this "init_dyn_addr" if it is not
> + * in use.

	if it is available.

> + *
> + * Therefore, i3c_bus_get_free_addr() should return a free address that has not been claimed by any

					preferably return

	that is not in the list of desired addresses.

> + * target devices as "init_dyn_addr". This allows the device with the "init_dyn_addr" to switch to
> + * its "init_dyn_addr" when it hot-joins the I3C bus. Otherwise, if the "init_dyn_addr" is already
> + * in use by another I3C device, the target device will not be able to switch to its desired
> + * address.
> + *
> + * If all of above address are already used, i3c_bus_get_free_addr() return one from the claimed as
> + * init_dyn_addr and free address slot. This ensures support devices as much as possible.

If the previous step fails, fallback returning one of the remaining
unassigned address, regardless of its state in the desired list.

> + */

Please update your commit message as well with these changes.

>  static int i3c_bus_get_free_addr(struct i3c_bus *bus, u8 start_addr)
>  {
>  	enum i3c_addr_slot_status status;
>  	u8 addr;
>  
> +	for (addr = start_addr; addr < I3C_MAX_ADDR; addr++) {
> +		status = i3c_bus_get_addr_slot_status_ext(bus, addr);

So here it could look like:

		status = ...get_addr_slot_status(bus, addr, <extended>)

> +		if (status == I3C_ADDR_SLOT_FREE)
> +			return addr;
> +	}
> +
>  	for (addr = start_addr; addr < I3C_MAX_ADDR; addr++) {
>  		status = i3c_bus_get_addr_slot_status(bus, addr);
>  		if (status == I3C_ADDR_SLOT_FREE)
> @@ -1918,9 +1968,9 @@ static int i3c_master_bus_init(struct i3c_master_controller *master)
>  			goto err_rstdaa;
>  		}
>  
> -		i3c_bus_set_addr_slot_status(&master->bus,
> -					     i3cboardinfo->init_dyn_addr,
> -					     I3C_ADDR_SLOT_I3C_DEV);
> +		i3c_bus_set_addr_slot_status_ext(&master->bus,
> +						 i3cboardinfo->init_dyn_addr,
> +						 I3C_ADDR_SLOT_I3C_DEV | I3C_ADDR_SLOT_EXT_INIT);
>  
>  		/*
>  		 * Only try to create/attach devices that have a static
> diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
> index 2100547b2d8d2..57ad6044ac856 100644
> --- a/include/linux/i3c/master.h
> +++ b/include/linux/i3c/master.h
> @@ -298,7 +298,8 @@ enum i3c_open_drain_speed {
>   * @I3C_ADDR_SLOT_I2C_DEV: address is assigned to an I2C device
>   * @I3C_ADDR_SLOT_I3C_DEV: address is assigned to an I3C device
>   * @I3C_ADDR_SLOT_STATUS_MASK: address slot mask
> - *
> + * @I3C_ADDR_SLOT_EXT_INIT: the bitmask represents addresses that are preferred by some devices,
> + *			    such as the "assigned-address" property in a device tree source (DTS).

The naming could be improved, because "extended" does not mean much. I
believe we should express the fact that this is a desired addressed, so
what about:

	I3C_ADDR_SLOT_I3C_ASSIGNED/DESIRED

>   * On an I3C bus, addresses are assigned dynamically, and we need to know which
>   * addresses are free to use and which ones are already assigned.
>   *
> @@ -311,9 +312,11 @@ enum i3c_addr_slot_status {
>  	I3C_ADDR_SLOT_I2C_DEV,
>  	I3C_ADDR_SLOT_I3C_DEV,
>  	I3C_ADDR_SLOT_STATUS_MASK = 3,
> +	I3C_ADDR_SLOT_EXT_STATUS_MASK = 7,
> +	I3C_ADDR_SLOT_EXT_INIT = BIT(2),
>  };
>  
> -#define I3C_ADDR_SLOT_STATUS_BITS 2
> +#define I3C_ADDR_SLOT_STATUS_BITS 4
>  
>  /**
>   * struct i3c_bus - I3C bus object
> 


Thanks,
Miquèl