Re: [PATCH v3 3/3] i3c: master: Validate GET CCC payload length and retry M0/M2 once

On 20/6/2026 3:28 am, Frank Li wrote:
> On Wed, Jun 10, 2026 at 06:54:08PM -0700, [email protected] wrote:
>> From: Adrian Ng Ho Yin <[email protected]>
>>
>> Validate GET CCC payload length after a successful transfer. Treat a
>> short read as I3C_ERROR_M0 and return -EIO. GETMRL accepts exactly 2 or
>> 3 bytes per the I3C spec defined formats. GETMXDS may return 2 bytes
>> (format 1) or 5 bytes (format 2) per I3C spec.
>>
>> Retry GET CCCs once on retriable errors: I3C_ERROR_M0 (frame error) and
>> I3C_ERROR_M2 (address-header NACK, e.g. IBI or Controller Role Request
>> arbitration per I3C spec section 5.1.2.2.3). SET CCCs are not retried
>> to avoid repeating side-effecting commands. Restore dests[].payload.len
>> to the originally requested length before each attempt and again before
>> returning an error, so callers that adjust the length on failure (e.g.
>> i3c_master_getmxds_locked()) do not underflow a shortened value.
>>
>> Use a stack buffer for the common single-destination GET case and only
>> kmalloc when ndests > 1.
>>
>> Signed-off-by: Adrian Ng Ho Yin <[email protected]>
>> Signed-off-by: Tze Yee Ng <[email protected]>
>> ---
>> Changes in v3:
>> - Drop the change that moves RESPONSE_ERROR_ADDRESS_NACK to default case
>>    in dw_i3c_master_end_xfer_locked(). Now dw_i3c_master_end_xfer_locked()
>>    returns -EIO for RESPONSE_ERROR_ADDRESS_NACK.
>> ---
>>   drivers/i3c/master.c | 111 ++++++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 110 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
>> index 5cd4e5da2233..c94d37cd8b3f 100644
>> --- a/drivers/i3c/master.c
>> +++ b/drivers/i3c/master.c
>> @@ -26,6 +26,12 @@ static DEFINE_MUTEX(i3c_core_lock);
>>   static int __i3c_first_dynamic_bus_num;
>>   static BLOCKING_NOTIFIER_HEAD(i3c_bus_notifier);
>>
>> +#define I3C_CCC_GETMRL_LEN_SHORT	2
>> +#define I3C_CCC_GETMRL_LEN_FULL		3
>> +#define I3C_CCC_GETMXDS_LEN_SHORT	2
>> +#define I3C_CCC_GETMXDS_LEN_FULL	5
>> +#define I3C_CCC_MAX_RETRIES	2
>> +
>>   /**
>>    * i3c_bus_maintenance_lock - Lock the bus for a maintenance operation
>>    * @bus: I3C bus to take the lock on
>> @@ -925,6 +931,61 @@ static void i3c_ccc_cmd_init(struct i3c_ccc_cmd *cmd, bool rnw, u8 id,
>>   	cmd->err = I3C_ERROR_UNKNOWN;
>>   }
>>
>> +static bool i3c_ccc_get_payload_ok(u8 id, u16 req_len, u16 actual_len)
>> +{
>> +	if (actual_len > req_len)
>> +		return false;
>> +
>> +	if (!req_len)
>> +		return actual_len == 0;
>> +
>> +	if (id == I3C_CCC_GETMRL)
>> +		return actual_len == I3C_CCC_GETMRL_LEN_SHORT ||
>> +		       actual_len == I3C_CCC_GETMRL_LEN_FULL;
>> +
>> +	if (id == I3C_CCC_GETMXDS)
>> +		return actual_len == I3C_CCC_GETMXDS_LEN_SHORT ||
>> +		       actual_len == I3C_CCC_GETMXDS_LEN_FULL;
>> +
>> +	return actual_len == req_len;
>> +}
>> +
>> +static int i3c_ccc_validate_payload_len(struct i3c_ccc_cmd *cmd,
>> +					const u16 *req_lens)
>> +{
>> +	unsigned int i;
>> +
>> +	if (!cmd->rnw)
>> +		return 0;
>> +
>> +	for (i = 0; i < cmd->ndests; i++) {
>> +		u16 actual = cmd->dests[i].payload.len;
>> +		u16 req = req_lens[i];
>> +
>> +		if (!i3c_ccc_get_payload_ok(cmd->id, req, actual)) {
>> +			cmd->err = I3C_ERROR_M0;
>> +			return -EIO;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * M0: transient frame errors.
>> + * M2: address-header NACK (I3C spec section 5.1.2.2.3), e.g. when a target
>> + *     simultaneously asserts an IBI or Controller Role Request and neither
>> + *     side ACKs. Software should re-issue the transfer; the controller wins
>> + *     arbitration after Repeated START.
>> + *
>> + * Retries apply to GET CCCs only; SET CCCs are not retried to avoid
>> + * repeating side-effecting commands.
>> + */
>> +static bool i3c_ccc_err_retriable(enum i3c_error_code err)
>> +{
>> +	return err == I3C_ERROR_M0 || err == I3C_ERROR_M2;
>> +}
>> +
>>   /**
>>    * i3c_master_send_ccc_cmd_locked() - send a CCC (Common Command Codes)
>>    * @master: master used to send frames on the bus
>> @@ -936,9 +997,17 @@ static void i3c_ccc_cmd_init(struct i3c_ccc_cmd *cmd, bool rnw, u8 id,
>>   static int i3c_master_send_ccc_cmd_locked(struct i3c_master_controller *master,
>>   					  struct i3c_ccc_cmd *cmd)
>>   {
>> +	u16 req_len;
>> +	u16 *req_lens = NULL;
>> +	u16 *req_lens_alloc = NULL;
>> +	unsigned int i;
>> +	int ret, retries;
>> +
>>   	if (!cmd || !master)
>>   		return -EINVAL;
>>
>> +	retries = cmd->rnw ? I3C_CCC_MAX_RETRIES : 1;
>> +
>>   	if (WARN_ON(master->init_done &&
>>   		    !rwsem_is_locked(&master->bus.lock)))
>>   		return -EINVAL;
>> @@ -953,7 +1022,47 @@ static int i3c_master_send_ccc_cmd_locked(struct i3c_master_controller *master,
>>   	    !master->ops->supports_ccc_cmd(master, cmd))
>>   		return -EOPNOTSUPP;
>>
>> -	return master->ops->send_ccc_cmd(master, cmd);
>> +	if (cmd->rnw && cmd->dests && cmd->ndests) {
>> +		if (cmd->ndests == 1) {
>> +			req_len = cmd->dests[0].payload.len;
>> +			req_lens = &req_len;
>> +		} else {
>> +			req_lens_alloc = kmalloc_array(cmd->ndests,
>> +						       sizeof(*req_lens_alloc),
>> +						       GFP_KERNEL);
>> +			if (!req_lens_alloc)
>> +				return -ENOMEM;
>> +
>> +			req_lens = req_lens_alloc;
>> +			for (i = 0; i < cmd->ndests; i++)
>> +				req_lens[i] = cmd->dests[i].payload.len;
>> +		}
>> +	}
>> +
>> +	do {
>> +		cmd->err = I3C_ERROR_UNKNOWN;
>> +		if (req_lens) {
>> +			for (i = 0; i < cmd->ndests; i++)
>> +				cmd->dests[i].payload.len = req_lens[i];
>> +		}
>> +		ret = master->ops->send_ccc_cmd(master, cmd);
> 
> why need retry here?
> 
> Frank
> 
Hi Frank,

Retry is required for Direct GET CCC per section 5.1.9.2.3 (section 
5.2.1.2.3 in HDR): if a target cannot respond to a Direct GET CCC on the 
first attempt, the master shall follow the SDR Direct GET retry model 
(typically one retry); the target should generally respond on the second 
attempt. Section 5.2.1.2.3 states the same for HDR Direct GET CCC. For 
Direct SET CCC, decline may mean the CCC/defining byte is unsupported, 
so the retry model does not necessarily apply — we will not auto-retry 
SET.>> +		if (!ret && req_lens)
>> +			ret = i3c_ccc_validate_payload_len(cmd, req_lens);
>> +	} while (--retries && ret && i3c_ccc_err_retriable(cmd->err));
>> +
>> +	if (ret && req_lens) {
>> +		/*
>> +		 * Drivers may update payload.len to the actual RX count;
>> +		 * restore the requested length so callers can safely adjust
>> +		 * it on error (e.g. i3c_master_getmxds_locked()).
>> +		 */
>> +		for (i = 0; i < cmd->ndests; i++)
>> +			cmd->dests[i].payload.len = req_lens[i];
>> +	}
>> +
>> +	kfree(req_lens_alloc);
>> +
>> +	return ret;
>>   }
>>
>>   static struct i2c_dev_desc *
>> --
>> 2.43.7
>>

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