linux-kernel - Re: [RFC v1 2/2] PCI: tegra: Use readl_poll

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CANAwSgT615R32WTBzi2-8FYntmaxbmVRLmA3yi+=4ryH43aaWQ@mail.gmail.com>
Date: Wed, 17 Sep 2025 13:15:38 +0530
From: Anand Moon <linux.amoon@...il.com>
To: Mikko Perttunen <mperttunen@...dia.com>
Cc: Thierry Reding <thierry.reding@...il.com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Manivannan Sadhasivam <mani@...nel.org>, Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Jonathan Hunter <jonathanh@...dia.com>, 
	"open list:PCI DRIVER FOR NVIDIA TEGRA" <linux-tegra@...r.kernel.org>, 
	"open list:PCI DRIVER FOR NVIDIA TEGRA" <linux-pci@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v1 2/2] PCI: tegra: Use readl_poll_timeout() for link status polling

Hi Mikko,

Thanks for your review comments.

On Wed, 17 Sept 2025 at 08:51, Mikko Perttunen <mperttunen@...dia.com> wrote:
>
> On Monday, September 1, 2025 4:00 AM Anand Moon wrote:
> > Replace the manual `do-while` polling loops with the readl_poll_timeout()
> > helper when checking the link DL_UP and DL_LINK_ACTIVE status bits
> > during link bring-up. This simplifies the code by removing the open-coded
> > timeout logic in favor of the standard, more robust iopoll framework.
> > The change improves readability and reduces code duplication.
> >
> > Cc: Thierry Reding <thierry.reding@...il.com>
> > Signed-off-by: Anand Moon <linux.amoon@...il.com>
> > ---
> >  drivers/pci/controller/pci-tegra.c | 38 ++++++++++++------------------
> >  1 file changed, 15 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
> > index 3841489198b64..8e850f7c84e40 100644
> > --- a/drivers/pci/controller/pci-tegra.c
> > +++ b/drivers/pci/controller/pci-tegra.c
> > @@ -24,6 +24,7 @@
> >  #include <linux/irqchip/chained_irq.h>
> >  #include <linux/irqchip/irq-msi-lib.h>
> >  #include <linux/irqdomain.h>
> > +#include <linux/iopoll.h>
>
> There is already an iopoll.h include in this file, so this adds a duplicate.
>
Opps, I missed this in rebasing my code.

> >  #include <linux/kernel.h>
> >  #include <linux/init.h>
> >  #include <linux/module.h>
> > @@ -2157,37 +2158,28 @@ static bool tegra_pcie_port_check_link(struct tegra_pcie_port *port)
> >       value |= RP_PRIV_MISC_PRSNT_MAP_EP_PRSNT;
> >       writel(value, port->base + RP_PRIV_MISC);
> >
> > -     do {
> > -             unsigned int timeout = TEGRA_PCIE_LINKUP_TIMEOUT;
> > -
> > -             do {
> > -                     value = readl(port->base + RP_VEND_XP);
> > -
> > -                     if (value & RP_VEND_XP_DL_UP)
> > -                             break;
> > -
> > -                     usleep_range(1000, 2000);
> > -             } while (--timeout);
> > +     while (retries--) {
> > +             int err;
> >
> > -             if (!timeout) {
> > +             err = readl_poll_timeout(port->base + RP_VEND_XP, value,
> > +                                      value & RP_VEND_XP_DL_UP,
> > +                                      1000,
> > +                                      TEGRA_PCIE_LINKUP_TIMEOUT * 1000);
>
> The logic change here looks OK to me. This makes the timeout 200ms (TEGRA_PCIE_LINKUP_TIMEOUT is 200). Previously, the code looped 200 times with a 1 to 2ms sleep on each iteration. So the timeout could have been longer than 200ms previously, but not in a way that could be relied on.

You're right; the original usleep_range(1000, 2000) had a variable sleep time.
To replicate the worst-case behavior of the old loop, the
readl_poll_timeout should
use a delay_us of 1000 and a timeout_us that matches the original
maximum duration.
Since the previous code looped 200 times with a maximum 2ms sleep,
the correct timeout is 400ms, so update (TEGRA_PCIE_LINKUP_TIMEOUT * 2000).
or increase TEGRA_PCIE_LINKUP_TIMEOUT to 400.

Are these changes ok with you?

Thank
-Anand