Hi Rob,
On 30/10/2024 17:47, Rob Herring wrote:
On Wed, Oct 30, 2024 at 11:03 AM Dirk Behme <dirk.behme@xxxxxxxxx> wrote:
On 30.10.24 15:05, Rob Herring wrote:
On Wed, Oct 30, 2024 at 3:15 AM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
On Tue, Oct 29, 2024 at 8:35 PM Rob Herring <robh@xxxxxxxxxx> wrote:
On Tue, Oct 29, 2024 at 1:57 PM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
On Tue, Oct 29, 2024 at 7:48 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
One option is to define a trait for integers:
Yeah, but that doesn't feel like something I should do here. I imagine
other things might need the same thing. Perhaps the bindings for
readb/readw/readl for example. And essentially the crate:num already
has the trait I need. Shouldn't the kernel mirror that? I recall
seeing some topic of including crates in the kernel?
You can design the trait to look similar to traits in external crates.
We did that for FromBytes/AsBytes.
I assume you're referring to the PrimInt trait [1]? That trait doesn't
really let you get rid of the catch-all case, and it's not even
unreachable due to the u128 type.
It was num::Integer which seems to be similar.
[1]: https://docs.rs/num-traits/0.2.19/num_traits/int/trait.PrimInt.html
+1, one more thing to consider is whether it makes sense to define a
DT-only trait that holds all the types that can be a device property
(like `bool` too, not just the `Integer`s).
Then we can avoid e.g. `property_read_bool` and simply do it in `property_read`.
Is there no way to say must have traitA or traitB?
No. What should it do if you pass it something that implements both traits?
If you want a single function name, you'll need one trait.
I'm not sure I want that actually.
DT boolean is a bit special. A property not present is false.
Everything else is true. For example, 'prop = <0>' or 'prop =
"string"' are both true. I'm moving things in the kernel to be
stricter so that those cases are errors. I recently introduced
(of|device)_property_present() for that reason. There's no type
information stored in DT. At the DT level, it's all just byte arrays.
However, we now have all the type information for properties within
the schema. So eventually, I want to use that to warn on accessing
properties with the wrong type.
For example, I think I don't want this to work:
if dev.property_read(c_str!("test,i16-array"))? {
// do something
}
But instead have:
if dev.property_present(c_str!("test,i16-array")) {
// do something
}
I think we have "optional" properties which can be there (== true) or
not (== false). Let's assume for this example "test,i16-array" is such
kind of "optional" property. With what you gave above we need two
device tree accesses, then? One to check if it is there and one to
read the data:
Yes, lots of properties are optional especially since any new property
added has to be because the DT is an ABI.
let mut array = <empty_marker>;
if dev.property_present(c_str!("test,i16-array")) {
array = dev.property_read(c_str!("test,i16-array"))?;
}
?
Instead of these two accesses, I was thinking to use the error
property_read() will return if the optional property is not there to
just do one access:
let mut array = <empty_marker>;
if let Ok(val) = dev.property_read(c_str!("test,i16-array")) {
array = val;
}
(and ignore the error case as its irrelvant in the optional case)
Have I missed anything?
If you grep "_property_present", most if not all calls never need the
data. When you need the data, you read it and test for EINVAL if you
want to handle "not present". The overhead of parsing the data is not
nothing, so I think it is better to provide both.
The typical pattern in the C code is:
u32 val = DEFAULT_VALUE;
of_property_read_u32(node, "a-property", &val);
// val is now either the read property or the default. If the property
is required, then the error code needs to be checked.
Maybe we should have:
let val: u32 = dev.property_read_optional(c_str!("test,i16-array"),
DEFAULT_VALUE);
Or looks like Option<> could be used here?:
let val: u32 = dev.property_read(c_str!("test,i16-array"),
Option<DEFAULT_VALUE>);
One thing I'd like to improve is having fewer driver error messages
and a printk for a missing required property is a common one. We have
APIs like clk_get and clk_get_optional (which parse firmware
properties). The difference is the former prints an error message on
error case and the latter is silent.
Maybe something like [1]?
It uses 'None' for mandatory properties and 'Some(<default>)' for
optional properties. And gives an error only in case of a missing
manadatory property.
Best regards
Dirk
[1]
diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
index 4161e7534018a..d97ec2d13a0ba 100644
--- a/rust/kernel/device.rs
+++ b/rust/kernel/device.rs
@@ -214,12 +214,26 @@ pub fn property_match_string(&self, name: &CStr,
match_str: &CStr) -> Result<usi
/// Returns firmware property `name` scalar value
///
+ /// Option is None: The property is assumed to be mandatory and an
error
+ /// is returned if it is not found.
+ /// Option is Some(default): The property is optional and the
passed default
+ /// value is returned if it is not found.
+ ///
/// Valid types are i8, u8, i16, u16, i32, u32, i64, u64
- pub fn property_read<T: Copy>(&self, name: &CStr) -> Result<T> {
+ pub fn property_read<T: Copy>(&self, name: &CStr, default:
Option<T>) -> Result<T> {
let mut val: [T; 1] = unsafe { core::mem::zeroed() };
- Self::_property_read_array(&self, name, &mut val)?;
- Ok(val[0])
+ match Self::_property_read_array(&self, name, &mut val) {
+ Ok(()) => return Ok(val[0]),
+ Err(e) => match default {
+ Some(default) => return Ok(default),
+ None => {
+ dev_err!(self, "Failed to read mandatory property
'{}' with error {}\n",
+ name, e.to_errno());
+ Err(e)
+ }
+ },
+ }
}
/// Returns firmware property `name` array values
diff --git a/samples/rust/rust_driver_platform.rs
b/samples/rust/rust_driver_platform.rs
index 95c2908068623..f8fe0f554183d 100644
--- a/samples/rust/rust_driver_platform.rs
+++ b/samples/rust/rust_driver_platform.rs
@@ -50,10 +50,21 @@ fn probe(pdev: &mut platform::Device, info:
Option<&Self::IdInfo>) -> Result<Pin
let prop = dev.property_read_bool(c_str!("test,bool-prop"));
dev_info!(dev, "bool prop is {}\n", prop);
- let _prop = dev.property_read::<u32>(c_str!("test,u32-prop"))?;
- let prop: u32 = dev.property_read(c_str!("test,u32-prop"))?;
+ let _prop = dev.property_read::<u32>(c_str!("test,u32-prop"),
None)?;
+ let prop: u32 = dev.property_read(c_str!("test,u32-prop"), None)?;
dev_info!(dev, "'test,u32-prop' is {:#x}\n", prop);
+ // Assume 'test,u32-optional' is an optional property which
does not exist.
+ let prop: u32 = dev.property_read(c_str!("test,u32-optional"),
Some(0xdb))?;
+ // Should print the default 0xdb and give no error.
+ dev_info!(dev, "'test,u32-optional' default is {:#x}\n", prop);
+
+ // Assume 'test,u32-mandatory' is a mandatory property which
does not exist.
+ // Should print an error (but ignore it in this example).
+ match dev.property_read::<u32>(c_str!("test,u32-mandatory"),
None) {
+ _ => (),
+ }
+
let prop: [i16; 4] =
dev.property_read_array(c_str!("test,i16-array"))?;
dev_info!(dev, "'test,i16-array' is {:?}\n", prop);
dev_info!(
