linux-kernel - Re: [RFC net-next v2 3/5] net: phy: nxp-c45-tja11xx add MACsec support

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Message-ID: <d770a31a-dafe-e833-3a18-36e32e63a62e@oss.nxp.com>
Date:   Fri, 25 Aug 2023 17:12:14 +0300
From:   "Radu Pirea (OSS)" <radu-nicolae.pirea@....nxp.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Sabrina Dubroca <sd@...asysnail.net>, hkallweit1@...il.com,
        linux@...linux.org.uk, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, richardcochran@...il.com,
        sebastian.tobuschat@....com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next v2 3/5] net: phy: nxp-c45-tja11xx add MACsec
 support



On 25.08.2023 16:50, Andrew Lunn wrote:
>>>>> +static bool nxp_c45_rx_sc_valid(struct nxp_c45_secy *phy_secy,
>>>>> +				struct macsec_rx_sc *rx_sc)
>>>>> +{
>>>>> +	u16 port =  (__force u64)rx_sc->sci >> (ETH_ALEN * 8);
>>>>
>>>> u64 sci = be64_to_cpu((__force __be64)rx_sc->sci);
>>>
>>> why is the __force needed? What happens with a normal cast?
>>>
>>
>> Sparse will print warnings if __force is missing.
> 
> What is the warning? I just want to make sure __force is the correct
> solution, not that something has the wrong type and we should be
> fixing a design issue.

Let's consider the following example:
Function declaration:
static int nxp_c45_macsec_write(struct phy_device *phydev, u16 reg,
				u32 val)
Call without __force:
nxp_c45_macsec_write(ctx->phydev, sa_regs->txsa_ssci,
		     (u32)cpu_to_be32(ssci));

Warning:
drivers/net/phy/nxp-c45-tja11xx-macsec.c:803:39: warning: cast from 
restricted __be32

Even if I will write another function that takes an __be32 as parameter, 
I will need to silent sparse for phy_write_mmd calls.

And in the following example will cry because of sci_t to __be64 conversion:
u64 sci = be64_to_cpu((__force __be64)rx_sc->sci);


>         Andrew
>   

-- 
Radu P.