Messages in this thread Patch in this message | | | Date | Tue, 3 Jan 2023 10:02:51 +0100 | From | Lukasz Majewski <> | Subject | Re: [PATCH v3 1/3] dsa: marvell: Provide per device information about max frame size |
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Hi Andrew,
> > @@ -3548,7 +3548,9 @@ static int mv88e6xxx_get_max_mtu(struct > > dsa_switch *ds, int port) if (chip->info->ops->port_set_jumbo_size) > > return 10240 - VLAN_ETH_HLEN - EDSA_HLEN - > > ETH_FCS_LEN; else if (chip->info->ops->set_max_frame_size) > > - return 1632 - VLAN_ETH_HLEN - EDSA_HLEN - > > ETH_FCS_LEN; > > + return (max_t(int, chip->info->max_frame_size, > > 1632) > > + - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN); > > + > > return 1522 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN; > > I would also prefer if all this if/else logic is removed, and the code > simply returned chip->info->max_frame_size - VLAN_ETH_HLEN - > EDSA_HLEN - ETH_FCS_LEN; >
So then the mv88e6xxx_get_max_mtu shall look like:
WARN_ON_ONCE(!chip->info->max_frame_size)
if (chip->info->ops->port_set_jumbo_size) ... else return chip->info->max_frame_size - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;
Or shall I put WARN_ON_ONCE to the mv88e6xxx_probe() function?
The above approach is contrary to one proposed by Alexander, who wanted to improve the defensive approach in this driver (to avoid situation where the max_frame_size callback is not defined and max_frame_size member of *_info struct is not added by developer).
Which approach is the recommended one for this driver?
> > +++ b/drivers/net/dsa/mv88e6xxx/chip.h > > @@ -132,6 +132,7 @@ struct mv88e6xxx_info { > > unsigned int num_gpio; > > unsigned int max_vid; > > unsigned int max_sid; > > + unsigned int max_frame_size; > > It might be worth adding a comment here what this value actually > represents.
Ok. I will add proper comment.
> We don't want any mixups where the value already has the > frame checksum removed for example.
Could you be more specific here about this use case?
The max_frame_size is the maximal size of the ethernet frame for which the IC designer provided specified amount of RAM (it is a different value for different SoCs in the Link Street family).
> > Andrew
Best regards,
Lukasz Majewski
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