linux-kernel - Re: [RFC PATCH V2 1/4] pci: APM X-Gene PCIe controller driver

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Date:	Sat, 25 Jan 2014 21:11:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Tanmay Inamdar <tinamdar@....com>, devicetree@...r.kernel.org,
	Jon Masters <jcm@...hat.com>, linux-doc@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	patches <patches@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Rob Landley <rob@...dley.net>, linux-pci@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [RFC PATCH V2 1/4] pci: APM X-Gene PCIe controller driver

On Friday 24 January 2014 13:28:22 Tanmay Inamdar wrote:
> On Thu, Jan 16, 2014 at 5:10 PM, Tanmay Inamdar <tinamdar@....com> wrote:
> > On Wed, Jan 15, 2014 at 4:39 AM, Arnd Bergmann <arnd@...db.de> wrote:
> >> On Wednesday 15 January 2014, Tanmay Inamdar wrote:

> >>
> >>> +static void xgene_pcie_poll_linkup(struct xgene_pcie_port *port, u32 *lanes)
> >>> +{
> >>> +     void *csr_base = port->csr_base;
> >>> +     u32 val32;
> >>> +     u64 start_time, time;
> >>> +
> >>> +     /*
> >>> +      * A component enters the LTSSM Detect state within
> >>> +      * 20ms of the end of fundamental core reset.
> >>> +      */
> >>> +     msleep(XGENE_LTSSM_DETECT_WAIT);
> >>> +     port->link_up = 0;
> >>> +     start_time = jiffies;
> >>> +     do {
> >>> +             val32 = readl(csr_base + PCIECORE_CTLANDSTATUS);
> >>> +             if (val32 & LINK_UP_MASK) {
> >>> +                     port->link_up = 1;
> >>> +                     port->link_speed = PIPE_PHY_RATE_RD(val32);
> >>> +                     val32 = readl(csr_base + BRIDGE_STATUS_0);
> >>> +                     *lanes = val32 >> 26;
> >>> +             }
> >>> +             time = jiffies_to_msecs(jiffies - start_time);
> >>> +     } while ((!port->link_up) || (time <= XGENE_LTSSM_L0_WAIT));
> >>> +}
> >>
> >> Maybe another msleep() in the loop? It seems weird to first do an
> >> unconditional sleep but then busy-wait for the result.
> >
> > ok.
> 
> This loop can execute for maximum 4 msec. So putting msleep(1) won't
> get us much.
 
4 msec is still quite a long time for a busy loop that can be spent doing
useful work in another thread.

> >>
> >> Another general note: Your "compatible" strings are rather unspecific.
> >> Do you have a version number for this IP block? I suppose that it's related
> >> to one that has been used in other chips before, or will be used in future
> >> chips, if it's not actually licensed from some other company.
> >
> > I will have to check this.
> >
> 
> We have decided to stick with current compatible string for now.

Can you elaborate on your reasoning? Does this mean X-Gene is a one-off
product and you won't be doing any new chips based on the same hardware
components?

	Arnd
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