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SubjectRE: [PATCH v3 net-next] net: mana: Add a driver for Microsoft Azure Network Adapter (MANA)
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> From: David Miller <davem@davemloft.net>
> Sent: Thursday, April 8, 2021 4:46 PM
> ...
> > +struct gdma_msg_hdr {
> > + u32 hdr_type;
> > + u32 msg_type;
> > + u16 msg_version;
> > + u16 hwc_msg_id;
> > + u32 msg_size;
> > +} __packed;
> > +
> > +struct gdma_dev_id {
> > + union {
> > + struct {
> > + u16 type;
> > + u16 instance;
> > + };
> > +
> > + u32 as_uint32;
> > + };
> > +} __packed;
>
> Please don't use __packed unless absolutely necessary. It generates
> suboptimal code (byte at a time
> accesses etc.) and for many of these you don't even need it.

In the driver code, all the structs/unions marked by __packed are used to
talk with the hardware, so I think __packed is necessary here?

Do you think if it's better if we remove all the __packed, and add
static_assert(sizeof(struct XXX) == YYY) instead? e.g.

@@ -105,7 +105,8 @@ struct gdma_msg_hdr {
u16 msg_version;
u16 hwc_msg_id;
u32 msg_size;
-} __packed;
+};
+static_assert(sizeof(struct gdma_msg_hdr) == 16);

struct gdma_dev_id {
union {
Now I'm trying to figure out how other NIC drivers define structs/unions.

Thanks,
Dexuan

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