Messages in this thread | | | Date | Wed, 30 Aug 2023 13:06:39 +0100 | From | "Russell King (Oracle)" <> | Subject | Re: [RFC net-next v2 3/5] net: phy: nxp-c45-tja11xx add MACsec support |
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On Fri, Aug 25, 2023 at 03:50:06PM +0200, 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.
Hi Andrew,
rx_sc->sci is sci_t, which is defined as:
typedef u64 __bitwise sci_t;
Sparse documentation (Documentation/dev-tools/sparse.rst) states that:
"__bitwise" is a type attribute, so you have to do something like this:: ... which makes PM_SUSPEND and PM_RESUME "bitwise" integers (the "__force" is there because sparse will complain about casting to/from a bitwise type, but in this case we really _do_ want to force the conversion).
So basically, sci is a bitwise type, which means sparse gives it special properties that ensures it can only be operated on using similarly typed integers.
So, those __force casts are needed to convert sci to something else.
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