netdev - Re: [PATCH v2 net-next 3/7] net: dsa: sja1105: Switch to hardware operations for PTP

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Message-Id: <20190912.133753.1473374980190418320.davem@davemloft.net>
Date:   Thu, 12 Sep 2019 13:37:53 +0200 (CEST)
From:   David Miller <davem@...emloft.net>
To:     olteanv@...il.com
Cc:     f.fainelli@...il.com, vivien.didelot@...il.com, andrew@...n.ch,
        richardcochran@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 3/7] net: dsa: sja1105: Switch to hardware
 operations for PTP

From: Vladimir Oltean <olteanv@...il.com>
Date: Thu, 12 Sep 2019 11:17:11 +0100

> Hi Dave,
> 
> On 12/09/2019, David Miller <davem@...emloft.net> wrote:
>> From: Vladimir Oltean <olteanv@...il.com>
>> Date: Tue, 10 Sep 2019 04:34:57 +0300
>>
>>>  static int sja1105_ptp_adjfine(struct ptp_clock_info *ptp, long
>>> scaled_ppm)
>>>  {
>>>  	struct sja1105_private *priv = ptp_to_sja1105(ptp);
>>> +	const struct sja1105_regs *regs = priv->info->regs;
>>>  	s64 clkrate;
>>> +	int rc;
>>  ..
>>> -static int sja1105_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
>>> -{
>>> -	struct sja1105_private *priv = ptp_to_sja1105(ptp);
>>> +	rc = sja1105_spi_send_int(priv, SPI_WRITE, regs->ptpclkrate,
>>> +				  &clkrate, 4);
>>
>> You're sending an arbitrary 4 bytes of a 64-bit value.  This works on little
>> endian
>> but will not on big endian.
>>
>> Please properly copy this clkrate into a "u32" variable and pass that into
>> sja1105_spi_send_int().
>>
>> It also seems to suggest that you want to use abs() to perform that weird
>> centering around 1 << 31 calculation.
>>
>> Thank you.
>>
> 
> It looks 'wrong' but it isn't. The driver uses the 'packing' framework
> (lib/packing.c) which is endian-agnostic (converts between CPU and
> peripheral endianness) and operates on u64 as the CPU word size. On
> the contrary, u32 would not work with the 'packing' API in its current
> form, but I don't see yet any reasons to extend it (packing64,
> packing32 etc).

That's extremely unintuitive and makes auditing patches next to impossible.