On 14.10.23 18:15, FUJITA Tomonori wrote:

On Sat, 14 Oct 2023 14:54:30 +0000
Benno Lossin [off-list ref] wrote:

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On 14.10.23 12:32, FUJITA Tomonori wrote:

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On Sat, 14 Oct 2023 08:07:03 +0000
Benno Lossin [off-list ref] wrote:

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On 14.10.23 09:22, FUJITA Tomonori wrote:

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On Fri, 13 Oct 2023 21:31:16 +0000
Benno Lossin [off-list ref] wrote:

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+    /// the exclusive access for the duration of the lifetime `'a`.

In some other thread you mentioned that no lock is held for
`resume`/`suspend`, how does this interact with it?

The same quesiton, 4th time?

Yes, it is not clear to me from the code/safety comment alone why
this is safe. Please improve the comment such that that is the case.

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PHYLIB is implemented in a way that PHY drivers exlusively access to
phy_device during the callbacks.

As I suggested in a previous thread, it would be extremely helpful
if you add a comment on the `phy` abstractions module that explains
how `PHYLIB` is implemented. Explain that it takes care of locking
and other safety related things.

  From my understanding, the callers of suspend() try to call suspend()
for a device only once. They lock a device and get the current state
and update the sate, then unlock the device. If the state is a
paticular value, then call suspend(). suspend() and resume() are also
called where only one thread can access a device.

Maybe explain this in the docs? In the future, when I will come
into contact with this again, I will probably have forgotten this
conversation, but the docs are permanent and can be re-read.

You meant adding this to the code?  like dding this to Device's #
Safety comment?

I would not put it in the `# Safety` section. Instead, put this
information on the phy module itself (the `//!` comments at the very
top of the file). I also would suggest to not take the above paragraph
word by word, but to improve and extend it.

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Anyway,

phy_id()
state()
get_link()
is_autoneg_enabled()
is_autoneg_completed()

doesn't modify Self.

yes, these should all be `&self`.

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The rest modifies then need to be &mut self? Note that function like read_*
updates the C data structure.

What exactly does it update? In Rust there is interior mutability
which is used to implement mutexes. Interior mutability allows
you to modify values despite only having a `&T` (for more info
see [1]). Our `Opaque<T>` type uses this pattern as well (since
you get a `*mut T` from `&Opaque<T>`) and it is the job of the
abstraction writer to figure out what mutability to use.

[1]: https://doc.rust-lang.org/reference/interior-mutability.html

I have no idea what exactly `read_*` modifies on the C side.
Mapping C functions to `&self`, `&mut self` and other receiver types
is not obvious in all cases. I would focus more on the following aspect
of `&mut self` and `&self`:

Since `&mut self` is unique, only one thread per instance of `Self`
can call that function. So use this when the C side would use a lock.
(or requires that only one thread calls that code)

I guess that the rest are &mut self but let me continue to make sure.

I think that you already know that Device instance only was created in
the callbacks. Before the callbacks are called, PHYLIB holds
phydev->lock except for resume()/suspend(). As explained in the
previous mail, only one thread calls resume()/suspend().

The information in this paragraph would also fit nicely into the
phy module docs.

btw, methods in Device calling a C side function like mdiobus_read,
mdiobus_write, etc which never touch phydev->lock. Note that the c
side functions in resume()/suspned() methods don't touch phydev->lock
too.

There are two types how the methods in Device changes the C side data.

1. read/write/read_paged

They call the C side functions, mdiobus_read, mdiobus_write,
phy_read_paged, respectively.

phy_device has a pointer to mii_bus object. It has stats for
read/write. So everytime they are called, stats is updated.

I think for reading & updating some stats using `&self`
should be fine. `write` should probably be `&mut self`.

2. the rest

The C side functions in the rest of methods in Device updates some
members in phy_device like set_speed() method does.

Those setter functions should be `&mut self`.

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Since multiple `&self` references are allowed to coexist, you should
use this for functions which perform their own serialization/do not
require serialization.

just to be sure, the C side guarantees that only one reference exists.

I see, then the `from_raw` function should definitely return
a `&mut Device`. Note that you can still call `&T` functions
when you have a `&mut T`.

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If you cannot decide what certain function receivers should be, then
we can help you, but I would need more info on what the C side is doing.

If you need more info on the C side, please let me know.

What about these functions?
- resolve_aneg_linkmode
- genphy_soft_reset
- init_hw
- start_aneg
- genphy_read_status
- genphy_update_link
- genphy_read_lpa
- genphy_read_abilities

-- 
Cheers,
Benno