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

Radu Pirea (OSS)
2023-08-25T14:14:04Z

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.