Re: [PATCH v3] dp8393x: don't force 32-bit register access

[Mark Cave-Ayland]

On 05/07/2021 08:52, Mark Cave-Ayland wrote:

> I think the problem is because of the interaction of .impl.max_access_size = 2 and 
> the it_shift property specifying a stride of 4 bytes: when the 4 byte access is split 
> into 2 x 2 byte accesses then for a read reg = addr >> s->it_shift causes the second 
> access to be a duplicate of the first rather than containing zeros.

After some more experiments I'm fairly confident this is the issue: if you rely on 
applying it_shift within the MMIO access itself then you lose the zero extension of 
the result to the access size as done by the memory API.

I'll come up with a new version which I shall send as part of an updated and tested 
v2 of Phil's housekeeping patchset, since the endian changes were really helpful when 
studying the descriptors.


ATB,

Mark.