Re: [Intel-wired-lan] [PATCH net-next] ice: Add low latency Tx timestamp read

[Tony Nguyen <anthony.l.nguyen@intel.com>]

On 7/22/2022 8:36 AM, Karol Kolacinski wrote:
> E810 products can support low latency Tx timestamp register read.
> This requires usage of threaded IRQ instead of kthread to reduce the
> kthread start latency (spikes up to 20 ms).
> Add a check for the device capability and use the new method if
> supported.
> 
> Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
> ---

<snip>

> @@ -3121,6 +3123,24 @@ static irqreturn_t ice_misc_intr(int __always_unused irq, void *data)
>   	return ret;
>   }
>   
> +/**
> + * ice_misc_intr_thread_fn - misc interrupt thread function
> + * @irq: interrupt number
> + * @data: pointer to a q_vector
> + */
> +static irqreturn_t ice_misc_intr_thread_fn(int __always_unused irq, void *data)
> +{
> +	struct ice_pf *pf = (struct ice_pf *)data;

Cast shouldn't be needed.

> +	irqreturn_t ret = IRQ_HANDLED;
> +	bool irq_handled;
> +
> +	irq_handled = ice_ptp_process_ts(pf);
> +	if (!irq_handled)
> +		ret = IRQ_WAKE_THREAD;
> +
> +	return ret;
> +}
> +
>   /**
>    * ice_dis_ctrlq_interrupts - disable control queue interrupts
>    * @hw: pointer to HW structure

<snip>

> @@ -2171,16 +2170,17 @@ s8 ice_ptp_request_ts(struct ice_ptp_tx *tx, struct sk_buff *skb)
>   }
>   
>   /**
> - * ice_ptp_process_ts - Spawn kthread work to handle timestamps
> + * ice_ptp_process_ts - Process the PTP Tx timestamps
>    * @pf: Board private structure
>    *
> - * Queue work required to process the PTP Tx timestamps outside of interrupt
> - * context.
> + * Returns true if timestamps are processed.
>    */
> -void ice_ptp_process_ts(struct ice_pf *pf)
> +bool ice_ptp_process_ts(struct ice_pf *pf)
>   {
>   	if (pf->ptp.port.tx.init)
> -		kthread_queue_work(pf->ptp.kworker, &pf->ptp.port.tx.work);
> +		return ice_ptp_tx_tstamp(&pf->ptp.port.tx);
> +	else
> +		return false;

I believe preference is to remove the else and have an un-indented 
return false.

<snip>

> @@ -2587,38 +2588,113 @@ static int ice_write_phy_reg_e810(struct ice_hw *hw, u32 addr, u32 val)
>   }
>   
>   /**
> - * ice_read_phy_tstamp_e810 - Read a PHY timestamp out of the external PHY
> + * ice_read_phy_tstamp_ll_e810 - Read a PHY timestamp registers through the FW
> + * @hw: pointer to the HW struct
> + * @idx: the timestamp index to read
> + * @hi: 8 bit timestamp high value
> + * @lo: 32 bit timestamp low value
> + *
> + * Read a 8bit timestamp high value and 32 bit timestamp low value out of the
> + * timestamp block of the external PHY on the E810 device using the low latency
> + * timestamp read.
> + */
> +static int
> +ice_read_phy_tstamp_ll_e810(struct ice_hw *hw, u8 idx, u8 *hi, u32 *lo)
> +{
> +	u32 val;
> +	u8 i;
> +
> +	/* Write TS index to read to the PF register so the FW can read it */
> +	val = FIELD_PREP(TS_LL_READ_TS_IDX, idx) | TS_LL_READ_TS;
> +	wr32(hw, PF_SB_ATQBAL, val);
> +
> +	/* Read the register repeatedly until the FW provides us the TS */
> +	for (i = TS_LL_READ_RETRIES; i > 0; i--) {
> +		val = rd32(hw, PF_SB_ATQBAL);
> +
> +		/* When the bit is cleared, the TS is ready in the register */
> +		if (!(FIELD_GET(TS_LL_READ_TS, val))) {
> +			/* High 8 bit value of the TS is on the bits 16:23 */
> +			*hi = FIELD_GET(TS_LL_READ_TS_HIGH, val);
> +
> +			/* Read the low 32 bit value and set the TS valid bit */
> +			*lo = rd32(hw, PF_SB_ATQBAH) | TS_VALID;
> +			return 0;
> +		}
> +
> +		udelay(10);

CHECK: usleep_range is preferred over udelay; see 
Documentation/timers/timers-howto.rst

> +	}
> +
> +	/* FW failed to provide the TS in time */
> +	ice_debug(hw, ICE_DBG_PTP, "Failed to read PTP timestamp using low latency read\n");
> +	return -EINVAL;
> +}
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