Re: [PATCH 00/11] Add support for RaspberryPi RP1 PCI device using a DT overlay

Krzysztof Kozlowski
2024-08-22T09:50:43Z

On 22/08/2024 11:05, Andrea della Porta wrote:
> Hi Krzysztof,
>
> On 15:42 Wed 21 Aug , Krzysztof Kozlowski wrote:
>> On 20/08/2024 16:36, Andrea della Porta wrote:
>>> RP1 is an MFD chipset that acts as a south-bridge PCIe endpoint sporting
>>> a pletora of subdevices (i.e. Ethernet, USB host controller, I2C, PWM,
>>> etc.) whose registers are all reachable starting from an offset from the
>>> BAR address. The main point here is that while the RP1 as an endpoint
>>> itself is discoverable via usual PCI enumeraiton, the devices it contains
>>> are not discoverable and must be declared e.g. via the devicetree.
>>>
>>> This patchset is an attempt to provide a minimum infrastructure to allow
>>> the RP1 chipset to be discovered and perpherals it contains to be added
>>> from a devictree overlay loaded during RP1 PCI endpoint enumeration.
>>> Followup patches should add support for the several peripherals contained
>>> in RP1.
>>>
>>> This work is based upon dowstream drivers code and the proposal from RH
>>> et al. (see [1] and [2]). A similar approach is also pursued in [3].
>>
>> Looking briefly at findings it seems this was not really tested by
>> automation and you expect reviewers to find issues which are pointed out
>> by tools. That's not nice approach. Reviewer's time is limited, while
>> tools do it for free. And the tools are free - you can use them without
>> any effort.
>
> Sorry if I gave you that impression, but this is not obviously the case.

Just look at number of reports... so many sparse reports that I wonder
how it is not the case.

And many kbuild reports.

> I've spent quite a bit of time in trying to deliver a patchset that ease
> your and others work, at least to the best I can. In fact, I've used many
> of the checking facilities you mentioned before sending it, solving all
> of the reported issues, except the ones for which there are strong reasons
> to leave untouched, as explained below.
>
>>
>> It does not look like you tested the DTS against bindings. Please run
>> `make dtbs_check W=1` (see
>> Documentation/devicetree/bindings/writing-schema.rst or
>> https://www.linaro.org/blog/tips-and-tricks-for-validating-devicetree-sources-with-the-devicetree-schema/
>> for instructions).
>
> #> make W=1 dt_binding_check DT_SCHEMA_FILES=raspberrypi,rp1-gpio.yaml
> CHKDT Documentation/devicetree/bindings
> LINT Documentation/devicetree/bindings
> DTEX Documentation/devicetree/bindings/pinctrl/raspberrypi,rp1-gpio.example.dts
> DTC_CHK Documentation/devicetree/bindings/pinctrl/raspberrypi,rp1-gpio.example.dtb
>
> #> make W=1 dt_binding_check DT_SCHEMA_FILES=raspberrypi,rp1-clocks.yaml
> CHKDT Documentation/devicetree/bindings
> LINT Documentation/devicetree/bindings
> DTEX Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.example.dts
> DTC_CHK Documentation/devicetree/bindings/clock/raspberrypi,rp1-clocks.example.dtb
>
> I see no issues here, in case you've found something different, I kindly ask you to post
> the results.
>
> #> make W=1 CHECK_DTBS=y broadcom/rp1.dtbo
> DTC arch/arm64/boot/dts/broadcom/rp1.dtbo
> arch/arm64/boot/dts/broadcom/rp1.dtso:37.24-42.7: Warning (simple_bus_reg): /fragment@0/__overlay__/rp1@0/clk_xosc: missing or empty reg/ranges property
> arch/arm64/boot/dts/broadcom/rp1.dtso:44.26-49.7: Warning (simple_bus_reg): /fragment@0/__overlay__/rp1@0/macb_pclk: missing or empty reg/ranges property
> arch/arm64/boot/dts/broadcom/rp1.dtso:51.26-56.7: Warning (simple_bus_reg): /fragment@0/__overlay__/rp1@0/macb_hclk: missing or empty reg/ranges property
> arch/arm64/boot/dts/broadcom/rp1.dtso:14.15-173.5: Warning (avoid_unnecessary_addr_size): /fragment@0/__overlay__: unnecessary #address-cells/#size-cells without "ranges", "dma-ranges" or child "reg" property
>
> I believe that These warnings are unavoidable, and stem from the fact that this
> is quite a peculiar setup (PCI endpoint which dynamically loads platform driver
> addressable via BAR).
> The missing reg/ranges in the threee clocks are due to the simple-bus of the
> containing node to which I believe they should belong: I did a test to place

This is not the place where they belong. non-MMIO nodes should not be
under simple-bus.

> those clocks in the same dtso under root or /clocks node but AFAIK it doesn't
> seems to work. I could move them in a separate dtso to be loaded before the main

Well... who instantiates them? If they are in top-level, then
CLK_OF_DECLARE which is not called at your point?

You must instantiate clocks different way, since they are not part of
"rp1". That's another bogus DT description... external oscilator is not
part of RP1.

> one but this is IMHO even more cumbersome than having a couple of warnings in
> CHECK_DTBS.
> Of course, if you have any suggestion on how to improve it I would be glad to
> discuss.
> About the last warning about the address/size-cells, if I drop those two lines
> in the _overlay_ node it generates even more warning, so again it's a "don't fix"
> one.
>
>>
>> Please run standard kernel tools for static analysis, like coccinelle,
>> smatch and sparse, and fix reported warnings. Also please check for
>> warnings when building with W=1. Most of these commands (checks or W=1
>> build) can build specific targets, like some directory, to narrow the
>> scope to only your code. The code here looks like it needs a fix. Feel
>> free to get in touch if the warning is not clear.
>
> I didn't run those static analyzers since I've preferred a more "manual" aproach
> by carfeully checking the code, but I agree that something can escape even the
> more carefully executed code inspection so I will add them to my arsenal from
> now on. Thanks for the heads up.

I don't care if you do not run static analyzers if you produce good
code. But if you produce bugs which could have been easily spotted with
sparser, than it is different thing.

Start running static checkers instead of asking reviewers to do that.

>
>>
>> Please run scripts/checkpatch.pl and fix reported warnings. Then please
>> run `scripts/checkpatch.pl --strict` and (probably) fix more warnings.
>> Some warnings can be ignored, especially from --strict run, but the code
>> here looks like it needs a fix. Feel free to get in touch if the warning
>> is not clear.
>>
>
> Again, most of checkpatch's complaints have been addressed, the remaining
> ones I deemed as not worth fixing, for example:>
> #> scripts/checkpatch.pl --strict --codespell tmp/*.patch
>
> WARNING: please write a help paragraph that fully describes the config symbol
> #42: FILE: drivers/clk/Kconfig:91:
> +config COMMON_CLK_RP1
> + tristate "Raspberry Pi RP1-based clock support"
> + depends on PCI || COMPILE_TEST
> + depends on COMMON_CLK
> + help
> + Enable common clock framework support for Raspberry Pi RP1.
> + This mutli-function device has 3 main PLLs and several clock
> + generators to drive the internal sub-peripherals.
> +
>
> I don't understand this warning, the paragraph is there and is more or less similar
> to many in the same file that are already upstream. Checkpatch bug?
>
>
> CHECK: Alignment should match open parenthesis
> #1541: FILE: drivers/clk/clk-rp1.c:1470:
> + if (WARN_ON_ONCE(clock_data->num_std_parents > AUX_SEL &&
> + strcmp("-", clock_data->parents[AUX_SEL])))
>
> This would have worsen the code readability.
>
>
> WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
> #673: FILE: drivers/pinctrl/pinctrl-rp1.c:600:
> + return -ENOTSUPP;
>
> This I must investigate: I've already tried to fix it before sending the patchset
> but for some reason it wouldn't work, so I planned to fix it in the upcoming
> releases.
>
>
> WARNING: externs should be avoided in .c files
> #331: FILE: drivers/misc/rp1/rp1-pci.c:58:
> +extern char __dtbo_rp1_pci_begin[];
>
> True, but in this case we don't have a symbol that should be exported to other
> translation units, it just needs to be referenced inside the driver and
> consumed locally. Hence it would be better to place the extern in .c file.
>
>
> Apologies for a couple of other warnings that I could have seen in the first
> place, but honestly they don't seems to be a big deal (one typo and on over
> 100 chars comment, that will be fixed in next patch version).

Again, judging by number of reports from checkers that is a big deal,
because it is your task to run the tools.

Best regards,
Krzysztof