Re: [PATCH v6 00/11] PCI: Drop duplicated tracking of a pci_dev's bound driver

Bjorn Helgaas
2021-10-13T11:34:03Z

On Wed, Oct 13, 2021 at 12:26:42PM +0300, Andy Shevchenko wrote:
> On Wed, Oct 13, 2021 at 2:33 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Mon, Oct 04, 2021 at 02:59:24PM +0200, Uwe Kleine-König wrote:
>
> > I split some of the bigger patches apart so they only touched one
> > driver or subsystem at a time. I also updated to_pci_driver() so it
> > returns NULL when given NULL, which makes some of the validations
> > quite a bit simpler, especially in the PM code in pci-driver.c.
>
> It's a bit unusual. Other to_*_dev() are not NULL-aware IIRC.

It is a little unusual. I only found three of 77 that are NULL-aware:

to_moxtet_driver()
to_siox_driver()
to_spi_driver()

It seems worthwhile to me because it makes the patch and the resulting
code significantly cleaner. Here's one example without the NULL
check:

@@ -493,12 +493,15 @@ static void pci_device_remove(struct device *dev)
static void pci_device_shutdown(struct device *dev)
{
struct pci_dev *pci_dev = to_pci_dev(dev);
- struct pci_driver *drv = pci_dev->driver;

pm_runtime_resume(dev);

- if (drv && drv->shutdown)
- drv->shutdown(pci_dev);
+ if (pci_dev->dev.driver) {
+ struct pci_driver *drv = to_pci_driver(pci_dev->dev.driver);
+
+ if (drv->shutdown)
+ drv->shutdown(pci_dev);
+ }

static void pci_device_shutdown(struct device *dev)
{
struct pci_dev *pci_dev = to_pci_dev(dev);

pm_runtime_resume(dev);

if (pci_dev->dev.driver) {
struct pci_driver *drv = to_pci_driver(pci_dev->dev.driver);

if (drv->shutdown)
drv->shutdown(pci_dev);
}

and here's the same thing with the NULL check:

@@ -493,7 +493,7 @@ static void pci_device_remove(struct device *dev)
static void pci_device_shutdown(struct device *dev)
{
struct pci_dev *pci_dev = to_pci_dev(dev);
- struct pci_driver *drv = pci_dev->driver;
+ struct pci_driver *drv = to_pci_driver(dev->driver);

static void pci_device_shutdown(struct device *dev)
{
struct pci_dev *pci_dev = to_pci_dev(dev);
struct pci_driver *drv = to_pci_driver(dev->driver);

pm_runtime_resume(dev);

if (drv && drv->shutdown)
drv->shutdown(pci_dev);

> > static bool match_id(struct pci_dev *pdev, unsigned short vendor, unsigned short device)
> > {
> > + struct pci_driver *drv = to_pci_driver(pdev->dev.driver);
> > const struct pci_device_id *id;
> >
> > if (pdev->vendor == vendor && pdev->device == device)
> > return true;
>
> > + for (id = drv ? drv->id_table : NULL; id && id->vendor; id++)
> > + if (id->vendor == vendor && id->device == device)
>
> > + break;
>
> return true;
>
> > return id && id->vendor;
>
> return false;

Good cleanup for a follow-up patch, but doesn't seem directly related
to the objective here. The current patch is:

@@ -80,7 +80,7 @@ static struct resource video_rom_resource = {
*/
static bool match_id(struct pci_dev *pdev, unsigned short vendor, unsigned short device)
{
- struct pci_driver *drv = pdev->driver;
+ struct pci_driver *drv = to_pci_driver(pdev->dev.driver);
const struct pci_device_id *id;

if (pdev->vendor == vendor && pdev->device == device)

> > device_lock(&vf_dev->dev);
> > - if (vf_dev->dev.driver) {
> > + if (to_pci_driver(vf_dev->dev.driver)) {
>
> Hmm...

Yeah, it could be either of:

if (to_pci_driver(vf_dev->dev.driver))
if (vf_dev->dev.driver)

I went back and forth on that and went with to_pci_driver() on the
theory that we were testing the pci_driver * before and the patch is
more of a mechanical change and easier to review if we test the
pci_driver * after.

> > + if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
>
> > + && pci_dev->current_state != PCI_UNKNOWN) {
>
> Can we keep && on the previous line?

I think this is in pci_legacy_suspend(), and I didn't touch that line.
It shows up in the interdiff because without the NULL check in
to_pci_driver(), we had to indent this code another level. With the
NULL check, we don't need that extra indentation.

> > + pci_WARN_ONCE(pci_dev, pci_dev->current_state != prev,
> > + "PCI PM: Device state not saved by %pS\n",
> > + drv->suspend);
> > }
>
> ...
>
> > + return drv && drv->resume ?
> > + drv->resume(pci_dev) : pci_pm_reenable_device(pci_dev);
>
> One line?

I don't think I touched that line.

> > + struct pci_driver *drv = to_pci_driver(dev->dev.driver);
> > const struct pci_error_handlers *err_handler =
> > - dev->dev.driver ? to_pci_driver(dev->dev.driver)->err_handler : NULL;
> > + drv ? drv->err_handler : NULL;
>
> Isn't dev->driver == to_pci_driver(dev->dev.driver)?

Yes, I think so, but not sure what you're getting at here, can you
elaborate?

> > device_lock(&dev->dev);
> > + pdrv = to_pci_driver(dev->dev.driver);
> > if (!pci_dev_set_io_state(dev, state) ||
> > - !dev->dev.driver ||
> > - !(pdrv = to_pci_driver(dev->dev.driver))->err_handler ||
>
> > + !pdrv ||
> > + !pdrv->err_handler ||
>
> One line now?
>
> > !pdrv->err_handler->error_detected) {
>
> Or this and the previous line?

Could, but the "dev->driver" to "to_pci_driver(dev->dev.driver)"
changes are the heart of this patch, and I don't like to clutter it
with unrelated changes.

> > - result = PCI_ERS_RESULT_NONE;
> >
> > pcidev = pci_get_domain_bus_and_slot(domain, bus, devfn);
> > if (!pcidev || !pcidev->dev.driver) {
> > dev_err(&pdev->xdev->dev, "device or AER driver is NULL\n");
> > pci_dev_put(pcidev);
> > - return result;
> > + return PCI_ERS_RESULT_NONE;
> > }
> > pdrv = to_pci_driver(pcidev->dev.driver);
>
> What about splitting the conditional to two with clear error message
> in each and use pci_err() in the second one?

Could possibly be cleaned up. Felt like feature creep so I didn't.

> > default:
> > dev_err(&pdev->xdev->dev,
> > - "bad request in aer recovery "
> > - "operation!\n");
> > + "bad request in AER recovery operation!\n");
>
> Stray change? Or is it in a separate patch in your tree?

Could be skipped. The string now fits on one line so I combined it to
make it more greppable.

Bjorn