linux-kernel - Re: [PATCH v3 7/8] PCI: Make minimum bridge window alignment reference more obvious

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Date: Tue, 7 May 2024 17:01:00 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Yury Norov <yury.norov@...il.com>
Cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/8] PCI: Make minimum bridge window alignment
 reference more obvious

On Tue, May 07, 2024 at 01:25:22PM +0300, Ilpo Järvinen wrote:
> Calculations related to bridge window size contain literal 20 that is
> the minimum alignment for a bridge window. Make the code more obvious
> by converting the literal 20 to __ffs(SZ_1MB).

..

> -		align1 <<= (order + 20);
> +		align1 <<= (order + __ffs(SZ_1M));

No need for outer parentheses.

..

> +			order = __ffs(align) - __ffs(SZ_1M);

Yeah, would be nice to have something like

#define bit_distance(a, b)	(ffs(a) - fls(b))

in bitops.h as we have a few users and I have heard about one more coming,
but this is topic to another discussion. (Yuri, just FYI.)

-- 
With Best Regards,
Andy Shevchenko