Re: [PATCH v3 2/4] Watchdog: sp5100_tco: Refactor MMIO base address initialization

[Guenter Roeck]

On 1/19/22 3:53 AM, Andy Shevchenko wrote:
> On Tue, Jan 18, 2022 at 10:23 PM Terry Bowman <terry.bowman@xxxxxxx> wrote:
> > Combine MMIO base address and alternate base address detection. Combine
> > based on layout type. This will simplify the function by eliminating
> > a switch case.
> >
> > Move existing request/release code into functions. This currently only
> > supports port I/O request/release. The move into a separate function
> > will make it ready for adding MMIO region support.
>
> ...
>
> > To: Guenter Roeck <linux@xxxxxxxxxxxx>
> > To: linux-watchdog@xxxxxxxxxxxxxxx
> > To: Jean Delvare <jdelvare@xxxxxxxx>
> > To: linux-i2c@xxxxxxxxxxxxxxx
> > To: Wolfram Sang <wsa@xxxxxxxxxx>
> > To: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> > To: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: Wim Van Sebroeck <wim@xxxxxxxxxxxxxxxxxx>
> > Cc: Robert Richter <rrichter@xxxxxxx>
> > Cc: Thomas Lendacky <thomas.lendacky@xxxxxxx>
>
> Same comment to all your patches.
>
> ...
>
> > +static int __sp5100_tco_prepare_base(struct sp5100_tco *tco,
> > +                                    u32 mmio_addr,
> > +                                    const char *dev_name)
> > +{
> > +       struct device *dev = tco->wdd.parent;
>
> > +       int ret = 0;
>
> Not really used variable.
>
> > +       if (!mmio_addr)
> > +               return -ENOMEM;
> > +
> > +       if (!devm_request_mem_region(dev, mmio_addr,
> > +                                   SP5100_WDT_MEM_MAP_SIZE,
> > +                                   dev_name)) {
> > +               dev_dbg(dev, "MMIO address 0x%08x already in use\n",
> > +                       mmio_addr);
> > +               return -EBUSY;
> > +       }
> > +
> > +       tco->tcobase = devm_ioremap(dev, mmio_addr,
> > +                                   SP5100_WDT_MEM_MAP_SIZE);

Talking about line splits, is this one necessary ?

> > +       if (!tco->tcobase) {
> > +               dev_dbg(dev, "MMIO address 0x%08x failed mapping.\n",
> > +                       mmio_addr);
>
> > +               devm_release_mem_region(dev, mmio_addr,
> > +                                       SP5100_WDT_MEM_MAP_SIZE);
>
> Why? If it's a short live mapping, do not use devm.

This is not short lived; it is needed by the driver. The release
is an artifact of calling this function twice and ignoring the error
from devm_ioremap() if the first call fails. devm_release_mem_region()
isn't strictly needed but that would result in keeping the memory
region reserved even though it isn't used by the driver.

There is a functional difference to the original code, though.
The failing devm_ioremap() causes the code to try the alternate
address. I am not sure if that really adds value; devm_ioremap()
fails because the system is out of virtual memory, and calling
it again on a different address doesn't seem to add much value.
I preferred the original code, which would only call devm_ioremap()
after successfully reserving a memory region.

> > +               return -ENOMEM;
> > +       }
>
> > +       dev_info(dev, "Using 0x%08x for watchdog MMIO address\n",
> > +                mmio_addr);
>
> Unneeded noise.
>
> > +       return ret;
>
> On top of above it's a NIH devm_ioremap_resource().

Not sure what NIH means, but if you refer to the lack of
devm_release_mem_region(), again, it isn't short lived.

> > +}
>
>
> ...
>
> > +       int ret = 0;
>
> Redundant assignment.
>
> ...
>
> > +       /* Check MMIO address conflict */
> > +       ret = __sp5100_tco_prepare_base(tco, mmio_addr, dev_name);
>
> > +
> > +       /* Check alternate MMIO address conflict */
>
> Unify this with the previous comment.

Why ? It refers to the code below. If that is a single or two comments
is really just POV.

> > +       if (ret)
> > +               ret = __sp5100_tco_prepare_base(tco, alt_mmio_addr,
> > +                                               dev_name);
>
> ...
>
> > +               if (alt_mmio_addr & ((SB800_ACPI_MMIO_DECODE_EN |
> > +                                     SB800_ACPI_MMIO_SEL) !=
> > +                                    SB800_ACPI_MMIO_DECODE_EN)) {
>
> The split looks ugly. Consider to use temporary variables or somehow
> rearrange the condition that it doesn't break in the middle of the one
> logical token.

Split at the &, maybe.

> > +                       alt_mmio_addr &= ~0xFFF;
>
> Why capital letters?
>
> > +                       alt_mmio_addr += SB800_PM_WDT_MMIO_OFFSET;
> > +               }
>
> ...
>
> > +               if (!(alt_mmio_addr & (((SB800_ACPI_MMIO_DECODE_EN |
> > +                                      SB800_ACPI_MMIO_SEL)) !=
> > +                     SB800_ACPI_MMIO_DECODE_EN))) {
>
> Ditto.
>
> > +                       alt_mmio_addr &= ~0xFFF;
>
> Ditto.
>
> > +                       alt_mmio_addr += SB800_PM_WDT_MMIO_OFFSET;
>
> ...
>
> Okay, I see this is the original code like this... Perhaps it makes
> sense to reshuffle them (indentation-wise) at the same time and
> mention this in the changelog.
>
> ...
>
> >          release_region(SP5100_IO_PM_INDEX_REG, SP5100_PM_IOPORTS_SIZE);
>
> Is it still needed? I have no context to say if devm_iomap() and this
> are not colliding, please double check the correctness.
Not sure I understand. This is the release of the io region reserved with
request_muxed_region() at the beginning of this function. Why would it no
longer be necessary to release that region ?

Guenter