Subject: Re: [PATCH net-next v17 01/13] rtase: Add pci table supported in this module

From: Simon Horman <[email-masked]>
Date: Wed, 8 May 2024 09:39:23 +0100

On Mon, May 06, 2024 at 11:32:38AM +0000, Justin Lai wrote:
> > 
> > 
> > On Thu, May 02, 2024 at 05:18:35PM +0800, Justin Lai wrote:
> > > Add pci table supported in this module, and implement pci_driver
> > > function to initialize this driver, remove this driver, or shutdown this driver.
> > >
> > > Signed-off-by: Justin Lai <[email-masked]>
> > 
> > ...
> > 
> > > diff --git a/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > b/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > new file mode 100644
> > > index 000000000000..5ddb5f7abfe9
> > > --- /dev/null
> > > +++ b/drivers/net/ethernet/realtek/rtase/rtase_main.c
> > > @@ -0,0 +1,618 @@
> > > +// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
> > > +/*
> > > + *  rtase is the Linux device driver released for Realtek Automotive
> > > +Switch
> > > + *  controllers with PCI-Express interface.
> > > + *
> > > + *  Copyright(c) 2023 Realtek Semiconductor Corp.
> > > + *
> > > + *  Below is a simplified block diagram of the chip and its relevant
> > interfaces.
> > > + *
> > > + *               *************************
> > > + *               *                       *
> > > + *               *  CPU network device   *
> > > + *               *                       *
> > > + *               *   +-------------+     *
> > > + *               *   |  PCIE Host  |     *
> > > + *               ***********++************
> > > + *                          ||
> > > + *                         PCIE
> > > + *                          ||
> > > + *      ********************++**********************
> > > + *      *            | PCIE Endpoint |             *
> > > + *      *            +---------------+             *
> > > + *      *                | GMAC |                  *
> > > + *      *                +--++--+  Realtek         *
> > > + *      *                   ||     RTL90xx Series  *
> > > + *      *                   ||                     *
> > > + *      *     +-------------++----------------+    *
> > > + *      *     |           | MAC |             |    *
> > > + *      *     |           +-----+             |    *
> > > + *      *     |                               |    *
> > > + *      *     |     Ethernet Switch Core      |    *
> > > + *      *     |                               |    *
> > > + *      *     |   +-----+           +-----+   |    *
> > > + *      *     |   | MAC |...........| MAC |   |    *
> > > + *      *     +---+-----+-----------+-----+---+    *
> > > + *      *         | PHY |...........| PHY |        *
> > > + *      *         +--++-+           +--++-+        *
> > > + *      *************||****************||***********
> > 
> > Thanks for the diagram, I like it a lot :)
> > 
> 
> Thank you for your like :)
> > > + *
> > > + *  The block of the Realtek RTL90xx series is our entire chip
> > > + architecture,
> > > + *  the GMAC is connected to the switch core, and there is no PHY in
> > between.
> > > + *  In addition, this driver is mainly used to control GMAC, but does
> > > + not
> > > + *  control the switch core, so it is not the same as DSA.
> > > + */
> > 
> > ...
> > 
> > > +static int rtase_alloc_msix(struct pci_dev *pdev, struct
> > > +rtase_private *tp) {
> > > +     int ret;
> > > +     u16 i;
> > > +
> > > +     memset(tp->msix_entry, 0x0, RTASE_NUM_MSIX * sizeof(struct
> > > + msix_entry));
> > > +
> > > +     for (i = 0; i < RTASE_NUM_MSIX; i++)
> > > +             tp->msix_entry[i].entry = i;
> > > +
> > > +     ret = pci_enable_msix_exact(pdev, tp->msix_entry, tp->int_nums);
> > > +     if (!ret) {
> > 
> > In Linux Networking code it is an idiomatic practice to keep handle errors in
> > branches and use the main path of execution for the non error path.
> > 
> > In this case I think that would look a bit like this:
> > 
> >         ret = pci_enable_msix_exact(pdev, tp->msix_entry, tp->int_nums);
> >         if (ret)
> >                 return ret;
> > 
> >         ...
> > 
> >         return 0;
> > 
> > > +
> > > +             for (i = 0; i < tp->int_nums; i++)
> > > +                     tp->int_vector[i].irq = pci_irq_vector(pdev, i);
> > 
> > pci_irq_vector() can fail, should that be handled here?
> 
> Thank you for your feedback, I will confirm this part again.
> > 
> > > +     }
> > > +
> > > +     return ret;
> > > +}
> > > +
> > > +static int rtase_alloc_interrupt(struct pci_dev *pdev,
> > > +                              struct rtase_private *tp) {
> > > +     int ret;
> > > +
> > > +     ret = rtase_alloc_msix(pdev, tp);
> > > +     if (ret) {
> > > +             ret = pci_enable_msi(pdev);
> > > +             if (ret)
> > > +                     dev_err(&pdev->dev,
> > > +                             "unable to alloc interrupt.(MSI)\n");
> > 
> > If an error occurs then it is a good practice to unwind resource allocations
> > made within the context of this function call, as this leads to more symmetric
> > unwind paths in callers.
> > 
> > In this case I think any resources consumed by rtase_alloc_msix() should be
> > released if pci_enable_msi fails. Probably using a goto label is appropriate
> > here.
> > 
> > Likewise, I suggest that similar logic applies to errors within
> > rtase_alloc_msix().
> > 
> 
> Since msi will be enabled only when msix enable fails, when pci_enable_msi fails,
> there will be no problem of msix-related resources needing to be released,
> because the msix interrupt has not been successfully allocated.

Thanks, as long as no allocated resources have not been freed in the case of
returning an error value, then I am happy.