Re: [PATCH v2 1/1] PCI: brcmstb: Use BIT() as __GENMASK() is for internal use only

Florian Fainelli
2021-11-16T20:57:56Z

On 11/16/21 12:41 PM, Florian Fainelli wrote:
> On 11/16/21 10:20 AM, Rob Herring wrote:
>> +Marc Z
>>
>> On Mon, Nov 15, 2021 at 8:39 AM Andy Shevchenko
>> <andriy.shevchenko@linux.intel.com> wrote:
>>>
>>> On Mon, Nov 15, 2021 at 04:14:21PM +0200, Andy Shevchenko wrote:
>>>> On Mon, Nov 15, 2021 at 4:01 PM Robin Murphy <robin.murphy@arm.com> wrote:
>>>>> On 2021-11-15 11:20, Andy Shevchenko wrote:
>>>>>> Use BIT() as __GENMASK() is for internal use only. The rationale
>>>>>> of switching to BIT() is to provide better generated code. The
>>>>>> GENMASK() against non-constant numbers may produce an ugly assembler
>>>>>> code. On contrary the BIT() is simply converted to corresponding shift
>>>>>> operation.
>>>>>
>>>>> FWIW, If you care about code quality and want the compiler to do the
>>>>> obvious thing, why not specify it as the obvious thing:
>>>>>
>>>>> u32 val = ~0 << msi->legacy_shift;
>>>>
>>>> Obvious and buggy (from the C standard point of view)? :-)
>>>
>>> Forgot to mention that BIT() is also makes it easy to avoid such mistake.
>>>
>>>>> Personally I don't think that abusing BIT() in the context of setting
>>>>> multiple bits is any better than abusing __GENMASK()...
>>>>
>>>> No, BIT() is not abused here, but __GENMASK().
>>>>
>>>> After all it's up to you, folks, consider that as a bug report.
>>
>> Couldn't we get rid of legacy_shift entirely if the legacy case sets
>> up 'hwirq' as 24-31 rather than 0-7? Though the data for the MSI msg
>> uses the hwirq.
>
> I personally find it clearer and easier to reason about with the current
> code though I suppose that with an appropriate xlate method we could
> sort of set up the hwirq the way we want them to be to avoid any
> shifting in brcm_pcie_msi_isr().

Something like the following maybe? Completely untested as I don't
believe I have a device with that legacy controller available at the moment:

diff --git a/drivers/pci/controller/pcie-brcmstb.c
b/drivers/pci/controller/pcie-brcmstb.c
index 1fc7bd49a7ad..41404b268fa3 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c
@@ -144,6 +144,8 @@
#define BRCM_INT_PCI_MSI_NR 32
#define BRCM_INT_PCI_MSI_LEGACY_NR 8
#define BRCM_INT_PCI_MSI_SHIFT 0
+#define BRCM_INT_PCI_MSI_MASK GENMASK(BRCM_INT_PCI_MSI_NR - 1, 0)
+#define BRCM_INT_PCI_MSI_LEGACY_MASK GENMASK(31, 32 -
BRCM_INT_PCI_MSI_LEGACY_NR)

/* MSI target addresses */
#define BRCM_MSI_TARGET_ADDR_LT_4GB 0x0fffffffcULL
@@ -269,8 +271,6 @@ struct brcm_msi {
/* used indicates which MSI interrupts have been alloc'd */
unsigned long used;
bool legacy;
- /* Some chips have MSIs in bits [31..24] of a shared register. */
- int legacy_shift;
int nr; /* No. of MSI available, depends on chip */
/* This is the base pointer for interrupt status/set/clr regs */
void __iomem *intr_base;
@@ -486,7 +486,6 @@ static void brcm_pcie_msi_isr(struct irq_desc *desc)
dev = msi->dev;

status = readl(msi->intr_base + MSI_INT_STATUS);
- status >>= msi->legacy_shift;

for_each_set_bit(bit, &status, msi->nr) {
int ret;
@@ -516,9 +515,8 @@ static int brcm_msi_set_affinity(struct irq_data
*irq_data,
static void brcm_msi_ack_irq(struct irq_data *data)
{
struct brcm_msi *msi = irq_data_get_irq_chip_data(data);
- const int shift_amt = data->hwirq + msi->legacy_shift;

- writel(1 << shift_amt, msi->intr_base + MSI_INT_CLR);
+ writel(BIT(data->hwirq), msi->intr_base + MSI_INT_CLR);
}

@@ -573,9 +571,31 @@ static void brcm_irq_domain_free(struct irq_domain
*domain,
brcm_msi_free(msi, d->hwirq);
}

+static int brcm_irq_domain_xlate(struct irq_domain *d,
+ struct device_node *node,
+ const u32 *intspec, unsigned int intsize,
+ unsigned long *out_hwirq,
+ unsigned int *out_type)
+{
+ struct brcm_msi *msi = d->host_data;
+
+ if (WARN_ON(intsize < 1))
+ return -EINVAL;
+
+ if (msi->legacy) {
+ *out_hwirq = intspec[0] + BRCM_INT_PCI_MSI_SHIFT;
+ *out_type = IRQ_TYPE_NONE;
+ return 0;
+ }
+
+ return irq_domain_xlate_onecell(d, node, intspec, intsize,
+ out_hwirq, out_type);
+}
+
static const struct irq_domain_ops msi_domain_ops = {
.alloc = brcm_irq_domain_alloc,
.free = brcm_irq_domain_free,
+ .xlate = brcm_irq_domain_xlate,
};

static int brcm_allocate_domains(struct brcm_msi *msi)
@@ -619,7 +639,8 @@ static void brcm_msi_remove(struct brcm_pcie *pcie)

static void brcm_msi_set_regs(struct brcm_msi *msi)
{
- u32 val = __GENMASK(31, msi->legacy_shift);
+ u32 val = msi->legacy ? BRCM_INT_PCI_MSI_MASK :
+ BRCM_INT_PCI_MSI_LEGACY_MASK;

writel(val, msi->intr_base + MSI_INT_MASK_CLR);
writel(val, msi->intr_base + MSI_INT_CLR);
@@ -664,11 +685,9 @@ static int brcm_pcie_enable_msi(struct brcm_pcie *pcie)
if (msi->legacy) {
msi->intr_base = msi->base + PCIE_INTR2_CPU_BASE;
msi->nr = BRCM_INT_PCI_MSI_LEGACY_NR;
- msi->legacy_shift = 24;
} else {
msi->intr_base = msi->base + PCIE_MSI_INTR2_BASE;
msi->nr = BRCM_INT_PCI_MSI_NR;
- msi->legacy_shift = 0;
}

ret = brcm_allocate_domains(msi);

--
Florian