Re: [PATCH 04/12] usb: dwc3: Expose core driver as library

Bjorn Andersson
2024-01-08T16:42:44Z

On Wed, Nov 22, 2023 at 12:57:37PM +0100, Johan Hovold wrote:
> On Mon, Oct 16, 2023 at 08:11:12PM -0700, Bjorn Andersson wrote:
> > The DWC3 IP block is handled by three distinct device drivers: XHCI,
> > DWC3 core and a platform specific (optional) DWC3 glue driver.
> >
> > This has resulted in, at least in the case of the Qualcomm glue, the
> > presence of a number of layering violations, where the glue code either
> > can't handle, or has to work around, the fact that core might not probe
> > deterministically.
> >
> > An example of this is that the suspend path should operate slightly
> > different depending on the device operating in host or peripheral mode,
> > and the only way to determine the operating state is to peek into the
> > core's drvdata.
> >
> > The Qualcomm glue driver is expected to make updates in the qscratch
> > register region (the "glue" region) during role switch events, but with
> > the glue and core split using the driver model, there is no reasonable
> > way to introduce listeners for mode changes.
> >
> > Split the dwc3 core platfrom_driver callbacks and their implementation
> > and export the implementation, to make it possible to deterministically
> > instantiate the dwc3 core as part of the dwc3 glue drivers and to
> > allow flattening of the DeviceTree representation.
> >
> > Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> > ---
> > drivers/usb/dwc3/core.c | 134 ++++++++++++++++++++++++++++++++----------------
> > drivers/usb/dwc3/core.h | 10 ++++
> > 2 files changed, 100 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index d25490965b27..71e376bebb16 100644
> > --- a/drivers/usb/dwc3/core.c
> > +++ b/drivers/usb/dwc3/core.c
> > @@ -1876,7 +1876,7 @@ static int dwc3_get_clocks(struct dwc3 *dwc)
> > return 0;
> > }
> >
> > -static int dwc3_probe(struct platform_device *pdev)
> > +struct dwc3 *dwc3_probe(struct platform_device *pdev)
>
> Perhaps you should move allocation of struct dwc3 to the caller as well
> as you are going to need some way to pass in callback to core which need
> to be set before you register the xhci platform device.
>
> There could be other ways, like passing in a struct of callbacks, which
> can be added incrementally but it may be good think this through from
> the start.
>

My intention was to have callbacks and quirks passed through additional
arguments in an incremental patch.

IMHO passing such information through a pre-allocated and partially
initialized struct is more obscure than passing that information as
explicit parameters to the function...

> > {
> > struct device *dev = &pdev->dev;
> > struct resource *res, dwc_res;
> > @@ -1886,14 +1886,14 @@ static int dwc3_probe(struct platform_device *pdev)
> >
> > dwc = devm_kzalloc(dev, sizeof(*dwc), GFP_KERNEL);
> > if (!dwc)
> > - return -ENOMEM;
> > + return ERR_PTR(-ENOMEM);
> >
> > dwc->dev = dev;
> >
> > res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > if (!res) {
> > dev_err(dev, "missing memory resource\n");
> > - return -ENODEV;
> > + return ERR_PTR(-ENODEV);
> > }
> >
> > dwc->xhci_resources[0].start = res->start;
> > @@ -1922,7 +1922,7 @@ static int dwc3_probe(struct platform_device *pdev)
> >
> > regs = devm_ioremap_resource(dev, &dwc_res);
> > if (IS_ERR(regs))
> > - return PTR_ERR(regs);
> > + return ERR_CAST(regs);
> >
> > dwc->regs = regs;
> > dwc->regs_size = resource_size(&dwc_res);
> > @@ -1953,7 +1953,6 @@ static int dwc3_probe(struct platform_device *pdev)
> > goto err_disable_clks;
> > }
> >
> > - platform_set_drvdata(pdev, dwc);
>
> This is broken however as the pm ops access the data driver data and can
> be called as soon as you call pm_runtime_put() below.
>

You're right, thanks for spotting that.

Regards,
Bjorn

> > dwc3_cache_hwparams(dwc);
> >
> > if (!dwc->sysdev_is_parent &&
> > @@ -2006,7 +2005,7 @@ static int dwc3_probe(struct platform_device *pdev)
> >
> > pm_runtime_put(dev);
>
> That is here.
>
> > - return 0;
> > + return dwc;
>
> > -static void dwc3_remove(struct platform_device *pdev)
> > +static int dwc3_plat_probe(struct platform_device *pdev)
> > {
> > - struct dwc3 *dwc = platform_get_drvdata(pdev);
> > + struct dwc3 *dwc;
> > +
> > + dwc = dwc3_probe(pdev);
> > + if (IS_ERR(dwc))
> > + return PTR_ERR(dwc);
>
> And that leaves a window, for example, here where you can hit a NULL
> pointer dereference.
>
> > + platform_set_drvdata(pdev, dwc);
> > +
> > + return 0;
> > +}
>
> Johan
>