From: Marc Zyngier <marc.zyngier@arm.com> To: Mason <slash.tmp@free.fr>, Bjorn Helgaas <helgaas@kernel.org>, Thomas Gleixner <tglx@linutronix.de> Cc: Robin Murphy <robin.murphy@arm.com>, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, Liviu Dudau <liviu.dudau@arm.com>, David Laight <david.laight@aculab.com>, linux-pci <linux-pci@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Thibaud Cornic <thibaud_cornic@sigmadesigns.com>, Phuong Nguyen <phuong_nguyen@sigmadesigns.com>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge Date: Fri, 24 Mar 2017 18:22:17 +0000 [thread overview] Message-ID: <6e847686-43c6-11e9-6782-dec0fe81a58e@arm.com> (raw) In-Reply-To: <9fffedd4-6292-b662-a588-a68fe7380af6@free.fr> On 23/03/17 23:40, Mason wrote: > On 23/03/2017 18:03, Mason wrote: > >> The host bridge actually supports 256 MSIs. >> >> IIUC, what you suggested on IRC is that I support 256 in the driver, >> and only read the status for *enabled* MSIs. >> >> Pseudo-code: >> >> for every 32-bit blob in the enabled bitmap >> if the value is non-zero >> lookup the corresponding status reg >> >> Problem is that a BITMAP is unsigned long (as you point out below). >> So I'm not sure how to iterate 32-bits at a time over the BITMAP. > > Something along these lines: > > DECLARE_BITMAP(enabled, 256); > > unsigned int pos = 0; > > while ((pos = find_next_bit(enabled, 256, pos)) < 256) { > int offset = (pos / 32) * 4; > u32 status = readl_relaxed(status + offset); > /* Handle each pos set in status */ > pos = round_up(pos, 32); > } Something along those lines, yes. > You mentioned a bug in my code (due to the platform endianness) > when passing the result of readl_relaxed to the bitops routine... > How is one supposed to iterate over status? You cannot directly use a pointer to a u32 in any of the bitmap operations. You need to copy the value to an unsigned long, and apply the bitmap op on that. > I'm not yet seeing this endianness issue, since (status & BIT(i)) > provides the status of MSI_i, irrespective of endianness. We discussed this over IRC, but I was referring to the above case and 64bit BE platforms, which would not do what you expect. > Although I see that arch/arm/include/asm/bitops.h declares > BE and LE variants... I'm confused. Nothing in this code should be ARM specific. The kernel gives you the tools to write (mostly) architecture, endianness and word size agnostic code. Thanks, M. -- Jazz is not dead. It just smells funny...
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From: marc.zyngier@arm.com (Marc Zyngier) To: linux-arm-kernel@lists.infradead.org Subject: [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge Date: Fri, 24 Mar 2017 18:22:17 +0000 [thread overview] Message-ID: <6e847686-43c6-11e9-6782-dec0fe81a58e@arm.com> (raw) In-Reply-To: <9fffedd4-6292-b662-a588-a68fe7380af6@free.fr> On 23/03/17 23:40, Mason wrote: > On 23/03/2017 18:03, Mason wrote: > >> The host bridge actually supports 256 MSIs. >> >> IIUC, what you suggested on IRC is that I support 256 in the driver, >> and only read the status for *enabled* MSIs. >> >> Pseudo-code: >> >> for every 32-bit blob in the enabled bitmap >> if the value is non-zero >> lookup the corresponding status reg >> >> Problem is that a BITMAP is unsigned long (as you point out below). >> So I'm not sure how to iterate 32-bits at a time over the BITMAP. > > Something along these lines: > > DECLARE_BITMAP(enabled, 256); > > unsigned int pos = 0; > > while ((pos = find_next_bit(enabled, 256, pos)) < 256) { > int offset = (pos / 32) * 4; > u32 status = readl_relaxed(status + offset); > /* Handle each pos set in status */ > pos = round_up(pos, 32); > } Something along those lines, yes. > You mentioned a bug in my code (due to the platform endianness) > when passing the result of readl_relaxed to the bitops routine... > How is one supposed to iterate over status? You cannot directly use a pointer to a u32 in any of the bitmap operations. You need to copy the value to an unsigned long, and apply the bitmap op on that. > I'm not yet seeing this endianness issue, since (status & BIT(i)) > provides the status of MSI_i, irrespective of endianness. We discussed this over IRC, but I was referring to the above case and 64bit BE platforms, which would not do what you expect. > Although I see that arch/arm/include/asm/bitops.h declares > BE and LE variants... I'm confused. Nothing in this code should be ARM specific. The kernel gives you the tools to write (mostly) architecture, endianness and word size agnostic code. Thanks, M. -- Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2017-03-24 18:25 UTC|newest] Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-03-23 13:05 [RFC PATCH v0.2] PCI: Add support for tango PCIe host bridge Mason 2017-03-23 13:05 ` Mason 2017-03-23 14:22 ` Marc Zyngier 2017-03-23 14:22 ` Marc Zyngier 2017-03-23 17:03 ` Mason 2017-03-23 17:03 ` Mason 2017-03-23 23:40 ` Mason 2017-03-23 23:40 ` Mason 2017-03-24 18:22 ` Marc Zyngier [this message] 2017-03-24 18:22 ` Marc Zyngier 2017-03-27 14:35 ` Mason 2017-03-27 14:35 ` Mason 2017-03-27 14:35 ` Mason 2017-03-27 14:46 ` Thomas Gleixner 2017-03-27 14:46 ` Thomas Gleixner 2017-03-27 15:18 ` Mason 2017-03-27 15:18 ` Mason 2017-03-27 15:18 ` Mason 2017-03-24 18:47 ` Marc Zyngier 2017-03-24 18:47 ` Marc Zyngier 2017-03-27 15:53 ` Mason 2017-03-27 15:53 ` Mason 2017-03-27 17:09 ` Marc Zyngier 2017-03-27 17:09 ` Marc Zyngier 2017-03-27 19:44 ` Mason 2017-03-27 19:44 ` Mason 2017-03-27 21:07 ` Marc Zyngier 2017-03-27 21:07 ` Marc Zyngier 2017-03-27 21:07 ` Marc Zyngier 2017-03-27 22:04 ` Mason 2017-03-27 22:04 ` Mason 2017-03-28 8:21 ` Marc Zyngier 2017-03-28 8:21 ` Marc Zyngier 2017-04-11 15:13 ` Mason 2017-04-11 15:13 ` Mason 2017-04-11 15:49 ` Marc Zyngier 2017-04-11 15:49 ` Marc Zyngier 2017-04-11 16:26 ` Mason 2017-04-11 16:26 ` Mason 2017-04-11 16:43 ` Marc Zyngier 2017-04-11 16:43 ` Marc Zyngier 2017-04-11 17:52 ` Mason 2017-04-11 17:52 ` Mason 2017-04-12 8:08 ` Marc Zyngier 2017-04-12 8:08 ` Marc Zyngier 2017-04-12 9:50 ` Mason 2017-04-12 9:50 ` Mason 2017-04-12 9:59 ` Marc Zyngier 2017-04-12 9:59 ` Marc Zyngier 2017-04-19 11:19 ` Mason 2017-04-19 11:19 ` Mason 2017-04-20 8:20 ` Mason 2017-04-20 8:20 ` Mason 2017-04-20 9:43 ` Marc Zyngier 2017-04-20 9:43 ` Marc Zyngier 2017-03-29 11:39 ` Mason 2017-03-29 11:39 ` Mason 2017-03-30 11:09 ` Mason 2017-03-30 11:09 ` Mason
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