linux-kernel - Re: [PATCH 3/4] net: wan: fsl_qmc_hdlc: Add runtime timeslots changes support

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Date: Wed, 24 Jan 2024 16:26:46 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, Andrew Lunn <andrew@...n.ch>, Mark Brown
 <broonie@...nel.org>, Christophe Leroy <christophe.leroy@...roup.eu>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 3/4] net: wan: fsl_qmc_hdlc: Add runtime timeslots
 changes support

Hi Vadim,

On Wed, 24 Jan 2024 10:10:46 +0000
Vadim Fedorenko <vadim.fedorenko@...ux.dev> wrote:

[...]
> > +static int qmc_hdlc_xlate_slot_map(struct qmc_hdlc *qmc_hdlc,
> > +				   u32 slot_map, struct qmc_chan_ts_info *ts_info)
> > +{
> > +	u64 ts_mask_avail;
> > +	unsigned int bit;
> > +	unsigned int i;
> > +	u64 ts_mask;
> > +	u64 map;
> > +
> > +	/* Tx and Rx masks must be identical */
> > +	if (ts_info->rx_ts_mask_avail != ts_info->tx_ts_mask_avail) {
> > +		dev_err(qmc_hdlc->dev, "tx and rx available timeslots mismatch (0x%llx, 0x%llx)\n",
> > +			ts_info->rx_ts_mask_avail, ts_info->tx_ts_mask_avail);
> > +		return -EINVAL;
> > +	}
> > +
> > +	ts_mask_avail = ts_info->rx_ts_mask_avail;
> > +	ts_mask = 0;
> > +	map = slot_map;
> > +	bit = 0;
> > +	for (i = 0; i < 64; i++) {
> > +		if (ts_mask_avail & BIT_ULL(i)) {
> > +			if (map & BIT_ULL(bit))
> > +				ts_mask |= BIT_ULL(i);
> > +			bit++;
> > +		}
> > +	}
> > +
> > +	if (hweight64(ts_mask) != hweight64(map)) {
> > +		dev_err(qmc_hdlc->dev, "Cannot translate timeslots 0x%llx -> (0x%llx,0x%llx)\n",
> > +			map, ts_mask_avail, ts_mask);
> > +		return -EINVAL;
> > +	}
> > +
> > +	ts_info->tx_ts_mask = ts_mask;
> > +	ts_info->rx_ts_mask = ts_mask;
> > +	return 0;
> > +}
> > +
> > +static int qmc_hdlc_xlate_ts_info(struct qmc_hdlc *qmc_hdlc,
> > +				  const struct qmc_chan_ts_info *ts_info, u32 *slot_map)
> > +{
> > +	u64 ts_mask_avail;
> > +	unsigned int bit;
> > +	unsigned int i;
> > +	u64 ts_mask;
> > +	u64 map;
> > +  
> 
> Starting from here ...
> 
> > +	/* Tx and Rx masks must be identical */
> > +	if (ts_info->rx_ts_mask_avail != ts_info->tx_ts_mask_avail) {
> > +		dev_err(qmc_hdlc->dev, "tx and rx available timeslots mismatch (0x%llx, 0x%llx)\n",
> > +			ts_info->rx_ts_mask_avail, ts_info->tx_ts_mask_avail);
> > +		return -EINVAL;
> > +	}
> > +	if (ts_info->rx_ts_mask != ts_info->tx_ts_mask) {
> > +		dev_err(qmc_hdlc->dev, "tx and rx timeslots mismatch (0x%llx, 0x%llx)\n",
> > +			ts_info->rx_ts_mask, ts_info->tx_ts_mask);
> > +		return -EINVAL;
> > +	}
> > +
> > +	ts_mask_avail = ts_info->rx_ts_mask_avail;
> > +	ts_mask = ts_info->rx_ts_mask;
> > +	map = 0;
> > +	bit = 0;
> > +	for (i = 0; i < 64; i++) {
> > +		if (ts_mask_avail & BIT_ULL(i)) {
> > +			if (ts_mask & BIT_ULL(i))
> > +				map |= BIT_ULL(bit);
> > +			bit++;
> > +		}
> > +	}
> > +
> > +	if (hweight64(ts_mask) != hweight64(map)) {
> > +		dev_err(qmc_hdlc->dev, "Cannot translate timeslots (0x%llx,0x%llx) -> 0x%llx\n",
> > +			ts_mask_avail, ts_mask, map);
> > +		return -EINVAL;
> > +	}
> > +  
> 
> till here the block looks like copy of the block from previous function.
> It worth to make a separate function for it, I think.
> 
> > +	if (map >= BIT_ULL(32)) {
> > +		dev_err(qmc_hdlc->dev, "Slot map out of 32bit (0x%llx,0x%llx) -> 0x%llx\n",
> > +			ts_mask_avail, ts_mask, map);
> > +		return -EINVAL;
> > +	}
> > +
> > +	*slot_map = map;
> > +	return 0;
> > +}
> > +
[...]

I am not so sure. There are slighty differences between the two functions.
The error messages and, in particular, the loop in qmc_hdlc_xlate_slot_map() is:
	--- 8< ---
	ts_mask_avail = ts_info->rx_ts_mask_avail;
	ts_mask = 0;
	map = slot_map;
	bit = 0;
	for (i = 0; i < 64; i++) {
		if (ts_mask_avail & BIT_ULL(i)) {
			if (map & BIT_ULL(bit))
				ts_mask |= BIT_ULL(i);
			bit++;
		}
	}
	--- 8< ---

whereas it is the following in qmc_hdlc_xlate_ts_info():
	--- 8< ---
	ts_mask_avail = ts_info->rx_ts_mask_avail;
	ts_mask = ts_info->rx_ts_mask;
	map = 0;
	bit = 0;
	for (i = 0; i < 64; i++) {
		if (ts_mask_avail & BIT_ULL(i)) {
			if (ts_mask & BIT_ULL(i))
				map |= BIT_ULL(bit);
			bit++;
		}
	}
	--- 8< ---

ts_map and map initializations are not the same, i and bit are not used for
the same purpose and the computed value is not computed based on the same
information.

With that pointed, I am not sure that having some common code for both
function will be relevant. Your opinion ?

Best regards,
Hervé