Date:   Thu, 28 Apr 2022 16:45:45 +0900
From:   Jung Daehwan <dh10.jung@...sung.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Howard Yen <howardyen@...gle.com>,
        Jack Pham <jackp@...eaurora.org>,
        Puma Hsu <pumahsu@...gle.com>,
        "J . Avila" <elavila@...gle.com>, sc.suh@...sung.com,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Subject: Re: [PATCH v4 5/5] usb: host: add xhci-exynos driver

On Thu, Apr 28, 2022 at 08:45:49AM +0200, Greg Kroah-Hartman wrote:
> On Thu, Apr 28, 2022 at 03:36:34PM +0900, Jung Daehwan wrote:
> > On Thu, Apr 28, 2022 at 07:19:04AM +0200, Krzysztof Kozlowski wrote:
> > > On 28/04/2022 03:29, Jung Daehwan wrote:
> > > > On Tue, Apr 26, 2022 at 02:59:57PM +0200, Krzysztof Kozlowski wrote:
> > > >> On 26/04/2022 11:18, Daehwan Jung wrote:
> > > >>> This driver is for Samsung Exynos xhci host conroller. It uses xhci-plat
> > > >>> driver mainly and extends some functions by xhci hooks and overrides.
> > > >>>
> > > >>> It supports USB Audio offload with Co-processor. It only cares DCBAA,
> > > >>> Device Context, Transfer Ring, Event Ring, and ERST. They are allocated
> > > >>> on specific address with xhci hooks. Co-processor could use them directly
> > > >>> without xhci driver after then.
> > > >>
> > > >> This does not look like developed in current Linux kernel, but something
> > > >> out-of-tree, with some other unknown modifications. This is not how the
> > > >> code should be developed. Please rebase on linux-next and drop any
> > > >> unrelated modifications (these which are not sent with this patchset).
> > > >>
> > > > 
> > > > I've been developing on linux-next and I rebase before submitting.
> > > > Could you tell me one of dropped modifications or patches?
> > > > 
> > > >> (...)
> > > >>
> > > >>> +
> > > >>> +static int xhci_exynos_suspend(struct device *dev)
> > > >>> +{
> > > >>> +	struct usb_hcd	*hcd = dev_get_drvdata(dev);
> > > >>> +	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> > > >>> +
> > > >>> +	/* TODO: AP sleep scenario*/
> > > >>
> > > >> Shall the patchset be called RFC?
> > > >>
> > > > OK. I will add RFC for this patch on next submission.
> > > > 
> > > >>> +
> > > >>> +	return xhci_suspend(xhci, device_may_wakeup(dev));
> > > >>> +}
> > > >>> +
> > > >>> +static int xhci_exynos_resume(struct device *dev)
> > > >>> +{
> > > >>> +	struct usb_hcd	*hcd = dev_get_drvdata(dev);
> > > >>> +	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
> > > >>> +	int ret;
> > > >>> +
> > > >>> +	/* TODO: AP resume scenario*/
> > > >>> +
> > > >>> +	ret = xhci_resume(xhci, 0);
> > > >>> +	if (ret)
> > > >>> +		return ret;
> > > >>> +
> > > >>> +	pm_runtime_disable(dev);
> > > >>> +	pm_runtime_set_active(dev);
> > > >>> +	pm_runtime_enable(dev);
> > > >>> +
> > > >>> +	return 0;
> > > >>> +}
> > > >>> +
> > > >>> +static const struct dev_pm_ops xhci_exynos_pm_ops = {
> > > >>> +	SET_SYSTEM_SLEEP_PM_OPS(xhci_exynos_suspend, xhci_exynos_resume)
> > > >>> +};
> > > >>> +
> > > >>> +MODULE_DESCRIPTION("xHCI Exynos Host Controller Driver");
> > > >>> +MODULE_LICENSE("GPL");
> > > >>
> > > >> You don't have list of compatibles (and missing bindings), driver
> > > >> definition, driver registration. Entire solution is not used - nothing
> > > >> calls xhci_exynos_vendor_init(), because nothign uses "ops".
> > > >>
> > > > 
> > > > xhci_exynos_vendor_init is called in xhci-plat.c (xhci_vendor_init)
> > > > [v4,2/5] usb: host: add xhci hooks for xhci-exynos
> > > > ops are used in some files(xhci-mem.c, xhci.c ..) and the body of ops is in
> > > > all xhci-exynos.
> > > 
> > > 
> > > Nothing uses the "ops" except xhci_exynos_register_vendor_ops() which is
> > > not called anywhere, so the xhci_vendor_init() does not call
> > > xhci_exynos_vendor_init().
> > > 
> > 
> > You are right. xhci_exynos_register_vendor_ops should be called by other
> > module. It's only thing not called anywhere in this patchset. I don't uses
> > xhci-exynos alone in my scenario. Other module loads this on runtime.
> > 
> > > > 
> > > > xhci-exynos is not a standalone driver. It could be enabled when other module
> > > > makes xhci platform driver probed as it uses xhci platform mainly.
> > > 
> > > It "could be" or "will be"? We do not talk here about theoretical usage
> > > of the driver, but a real one.
> > > 
> > > > I thought I just used existing compltible not adding new one.
> > > > I will add them if needed.
> > > 
> > > Since you called everything here as "exynos" it is specific to one
> > > hardware and not-reusable on anything else. How can then you use some
> > > other compatible? It would be a misuse of Devicetree bindings.
> > > 
> > 
> > I got it. Let me add them. Is it still necessary if it is only used by
> > other module on runtime as I said above?
> 
> Please submit a full, working driver so these changes can be able to be
> properly reviewed.  Otherwise it is just a waste of time for us to even
> read them, right?
> 
> We do not add changes to the kernel that do not work or do anything,
> that would be pointless, and cause us extra work and maintenance.
> 

We have several drivers including this and some drivers depends on other
drivers. I can't submit all drivers at the same time and It would be harder
if I did. That's why I submitted only patches in xhci without any dependancy.
I wanted to submit our all drivers one by one after then.
I will add it on next submission. New patch would be about dwc3-exynos.c not
in xhci.

I'm sorry to bother you but I hope you wouldn't think it's waste of time..

Best Regards,
Jung Daehwan

> thanks,
> 
> greg k-h
> 

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