From: Robin Murphy <robin.murphy@arm.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
bcm-kernel-feedback-list@broadcom.com,
linux-rpi-kernel@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: "Jim Quinlan" <jim2101024@gmail.com>,
"Nicolas Saenz Julienne" <nsaenz@kernel.org>,
"Florian Fainelli" <f.fainelli@gmail.com>,
"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
"Rob Herring" <robh@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Bjorn Helgaas" <bhelgaas@google.com>
Subject: Re: [PATCH v2 1/1] PCI: brcmstb: Use BIT() as __GENMASK() is for internal use only
Date: Mon, 15 Nov 2021 13:59:11 +0000 [thread overview]
Message-ID: <94d3f4e5-a698-134c-8264-55d31d3eafa6@arm.com> (raw)
In-Reply-To: <20211115112000.23693-1-andriy.shevchenko@linux.intel.com>
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;
Personally I don't think that abusing BIT() in the context of setting
multiple bits is any better than abusing __GENMASK()...
Robin.
> Note, it's the only user of __GENMASK() in the kernel outside of its own realm.
>
> Fixes: 3baec684a531 ("PCI: brcmstb: Accommodate MSI for older chips")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> v2: switched to BIT() and elaborated why, hence not included tag
> drivers/pci/controller/pcie-brcmstb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> index 1fc7bd49a7ad..0c49fc65792c 100644
> --- a/drivers/pci/controller/pcie-brcmstb.c
> +++ b/drivers/pci/controller/pcie-brcmstb.c
> @@ -619,7 +619,7 @@ 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 = ~(BIT(msi->legacy_shift) - 1);
>
> writel(val, msi->intr_base + MSI_INT_MASK_CLR);
> writel(val, msi->intr_base + MSI_INT_CLR);
>
next prev parent reply other threads:[~2021-11-15 14:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-15 11:20 [PATCH v2 1/1] PCI: brcmstb: Use BIT() as __GENMASK() is for internal use only Andy Shevchenko
2021-11-15 11:57 ` Krzysztof Wilczyński
2021-11-15 13:59 ` Robin Murphy [this message]
2021-11-15 14:14 ` Andy Shevchenko
2021-11-15 14:39 ` Andy Shevchenko
2021-11-16 18:20 ` Rob Herring
2021-11-16 20:41 ` Florian Fainelli
2021-11-16 20:56 ` Florian Fainelli
2021-11-17 10:37 ` Andy Shevchenko
2021-11-17 22:46 ` Rob Herring
2021-11-16 20:38 ` Florian Fainelli
2021-11-17 12:42 ` Andy Shevchenko
2021-12-01 15:53 ` Lorenzo Pieralisi
2021-12-01 16:01 ` Andy Shevchenko
2021-12-01 17:13 ` Lorenzo Pieralisi
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