Re: [PATCH v7 3/5] Add debugfs based silicon debug support in DWC

Geert Uytterhoeven
2025-03-06T09:34:05Z

Hi Krzysztof,

On Wed, 5 Mar 2025 at 20:10, Krzysztof Wilczyński <kw@linux.com> wrote:
> [...]
> > > > Even though debugfs_init() failure is not supposed to fail the probe(),
> > > > dwc_pcie_rasdes_debugfs_init() has a devm_kzalloc() and propagating that
> > > > failure would be canolically correct IMO.
> > >
> > > I'm not sure about this. What's the requirement to propagate
> > > devm_kzalloc() failures? I think devres will free any allocs that
> > > were successful regardless.
> > >
> > > IIUC, we resolved the Gray Hawk Single issue by changing
> > > dwc_pcie_rasdes_debugfs_init() to return success without doing
> > > anything when there's no RAS DES Capability.
> > >
> > > But dwc_pcie_debugfs_init() can still return failure, and that still
> > > causes dw_pcie_ep_init_registers() to fail, which breaks the "don't
> > > propagate debugfs issues upstream" rule:
> > >
> > > int dw_pcie_ep_init_registers(struct dw_pcie_ep *ep)
> > > {
> > > ...
> > > ret = dwc_pcie_debugfs_init(pci);
> > > if (ret)
> > > goto err_remove_edma;
> > >
> > > return 0;
> > >
> > > err_remove_edma:
> > > dw_pcie_edma_remove(pci);
> > >
> > > return ret;
> > > }
> > >
> > > We can say that kzalloc() failure should "never" happen, and therefore
> > > it's OK to fail the driver probe if it happens, but that doesn't seem
> > > like a strong argument for breaking the "don't propagate debugfs
> > > issues" rule. And someday there may be other kinds of failures from
> > > dwc_pcie_debugfs_init().

pcie-designware-debugfs.c only does small allocations. If any of
these fail, you have much bigger problems, and the system will die soon,
irrespective of propagating the -ENOMEM or not...

Another issue is that the caller does not handle failures correctly,
given (A) the irqdomain WARNING I got, and (B) the half-registered
PCI bus, oopsing on "lspci"...

> > Fine with me. I was not too sure about propagating failure either.
>
> What if we do this?
>
> diff --git i/drivers/pci/controller/dwc/pcie-designware-debugfs.c w/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> index 586a9d107434..fddf71f014c4 100644
> --- i/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> +++ w/drivers/pci/controller/dwc/pcie-designware-debugfs.c
> @@ -162,7 +162,7 @@ void dwc_pcie_debugfs_deinit(struct dw_pcie *pci)
> debugfs_remove_recursive(pci->debugfs->debug_dir);
> }
>
> -int dwc_pcie_debugfs_init(struct dw_pcie *pci)
> +void dwc_pcie_debugfs_init(struct dw_pcie *pci)
> {
> char dirname[DWC_DEBUGFS_BUF_MAX];
> struct device *dev = pci->dev;
> @@ -174,17 +174,15 @@ int dwc_pcie_debugfs_init(struct dw_pcie *pci)
> snprintf(dirname, DWC_DEBUGFS_BUF_MAX, "dwc_pcie_%s", dev_name(dev));
> dir = debugfs_create_dir(dirname, NULL);
> debugfs = devm_kzalloc(dev, sizeof(*debugfs), GFP_KERNEL);
> - if (!debugfs)
> - return -ENOMEM;
> + if (!debugfs) {
> + dev_err(dev, "failed to allocate memory for debugfs\n");

There is no need to print an error message when a memory allocation
fails, as the memory allocation core already takes care of that.
So please drop the dev_err() call.

> + return;
> + }
>

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds