From: Bjorn Helgaas <helgaas@kernel.org>
To: Muni Sekhar <munisekharrms@gmail.com>
Cc: linux-pci@vger.kernel.org
Subject: Re: PCIe: readl()
Date: Thu, 6 Jan 2022 16:18:56 -0600 [thread overview]
Message-ID: <20220106221856.GA328650@bhelgaas> (raw)
In-Reply-To: <CAHhAz+jFFqD=M=F8y6V_M1f6HDnBnzZDhOJt-G-pzWLHC4idFA@mail.gmail.com>
On Thu, Jan 06, 2022 at 10:43:52PM +0530, Muni Sekhar wrote:
> Hi all,
>
> We have a free-running counter on x86 PCIe bus and plan to use it as a
> clocksource. The 'read' field of the clocksource structure reads from
> this free-running counter and returns this value.
>
> Since PCIe reads are synchronous, is it safe to use readl() API to
> read this free-running counter value in struct clocksource.read()? If
> not, what's the best way to read the counter value from the struct
> clocksource read field?
Yes, you can use readl(). Of course, the driver for your PCIe device
will have to do the usual setup, e.g.,
probe(struct pci_dev *dev)
{
pci_request_regions(dev, "name");
addr = pci_ioremap_bar(dev, 0);
readl(addr);
The readl() should give you a single PCIe transaction, which is the
best you can do.
Bjorn
prev parent reply other threads:[~2022-01-06 22:18 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-06 17:13 PCIe: readl() Muni Sekhar
2022-01-06 22:18 ` Bjorn Helgaas [this message]
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