linux-kernel - RE: [PATCH v2] dwc: dra7xx: Print link state to console for debug

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Date:   Thu, 19 Oct 2017 13:26:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Faiz Abbas' <faiz_abbas@...com>, "kishon@...com" <kishon@...com>
CC:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] dwc: dra7xx: Print link state to console for debug

From: Faiz Abbas
> Sent: 19 October 2017 14:09
> On Thursday 19 October 2017 06:13 PM, Faiz Abbas wrote:
> > Enable support for printing the LTSSM link state for debugging PCI
> > when link is down.
> >
> > Signed-off-by: Faiz Abbas <faiz_abbas@...com>
> > ---
> > v2:
> >  1. Changed dev_err() to dev_dbg()
> >  2. Changed static char array to static const char * const
> >  3. format changes
> >
> >  drivers/pci/dwc/pci-dra7xx.c | 48 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 48 insertions(+)
> >
> > diff --git a/drivers/pci/dwc/pci-dra7xx.c b/drivers/pci/dwc/pci-dra7xx.c
> > index 34427a6..0e70e77 100644
> > --- a/drivers/pci/dwc/pci-dra7xx.c
> > +++ b/drivers/pci/dwc/pci-dra7xx.c
> > @@ -98,6 +98,45 @@ struct dra7xx_pcie_of_data {
> >
> >  #define to_dra7xx_pcie(x)	dev_get_drvdata((x)->dev)
> >
> > +static const char * const state[] = {
> > +	"DETECT_QUIET",
...
> > +	"RCVRY_EQ3"
> > +};
> > +
> >  static inline u32 dra7xx_pcie_readl(struct dra7xx_pcie *pcie, u32 offset)
> >  {
> >  	return readl(pcie->base + offset);
> > @@ -118,6 +157,15 @@ static int dra7xx_pcie_link_up(struct dw_pcie *pci)
> >  {
> >  	struct dra7xx_pcie *dra7xx = to_dra7xx_pcie(pci);
> >  	u32 reg = dra7xx_pcie_readl(dra7xx, PCIECTRL_DRA7XX_CONF_PHY_CS);
> > +	u32 cmd_reg;
> > +	u32 ltssm_state;
> > +
> > +	if (!(reg & LINK_UP)) {
> > +		cmd_reg = dra7xx_pcie_readl(dra7xx,
> > +					    PCIECTRL_DRA7XX_CONF_DEVICE_CMD);
> > +		ltssm_state = (cmd_reg & GENMASK(7, 2)) >> 2;
> > +		dev_dbg(pci->dev, "Link state:%s\n", state[ltssm_state]);

Hmmm... GENMASK leaves by hunting header files...
Why not (cmd_reg >> 2) & 63 and explicitly define state[64]
to guarantee that you never print anything worse than a NULL
pointer.

> > +	}
> >
> >  	return !!(reg & LINK_UP);
> >  }
> >
> 
> I missed David's comment in v1. Will submit a new version. Please ignore.

I've a 'neat' trick for generating strings that match constants.
You can get the compiler to do all the work for you:
(Assuming I've typed it correctly)

#define LTSSM_DEFS(x) \
  x(DETECT_QUIET) \
  x(DETECT_ACT) \
(continue for all the names)

Define an enum with the named constants:
#define X(name) LTSSM_STATE_##name,
enum (LTSSM_DEFS(X) LTSSM_STATE_SIZE=64);
#undef X

Array of strings:
#define X(name) [LTSSM_STATE_##name] = #name
static const char * const state_names[LTSSM_STATE_SIZE] = { LTSSM_DEFS(X) };
#undef X

	David