linux-kernel - RE: [PATCH v2 4/4] phy: zynqmp: Add debugfs support

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Message-ID:
 <MN0PR12MB595380A6FBC3B67B312E440CB7C22@MN0PR12MB5953.namprd12.prod.outlook.com>
Date: Fri, 14 Jun 2024 05:16:34 +0000
From: "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
To: Sean Anderson <sean.anderson@...ux.dev>, Laurent Pinchart
	<laurent.pinchart@...asonboard.com>, "linux-phy@...ts.infradead.org"
	<linux-phy@...ts.infradead.org>
CC: Vinod Koul <vkoul@...nel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Simek, Michal" <michal.simek@....com>,
	Kishon Vijay Abraham I <kishon@...nel.org>
Subject: RE: [PATCH v2 4/4] phy: zynqmp: Add debugfs support

> -----Original Message-----
> From: Sean Anderson <sean.anderson@...ux.dev>
> Sent: Thursday, June 13, 2024 8:32 PM
> To: Pandey, Radhey Shyam <radhey.shyam.pandey@....com>; Laurent
> Pinchart <laurent.pinchart@...asonboard.com>; linux-
> phy@...ts.infradead.org
> Cc: Vinod Koul <vkoul@...nel.org>; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org; Simek, Michal <michal.simek@....com>;
> Kishon Vijay Abraham I <kishon@...nel.org>
> Subject: Re: [PATCH v2 4/4] phy: zynqmp: Add debugfs support
> 
> On 6/13/24 05:20, Pandey, Radhey Shyam wrote:
> >> -----Original Message-----
> >> From: Sean Anderson <sean.anderson@...ux.dev>
> >> Sent: Monday, May 6, 2024 10:31 PM
> >> To: Laurent Pinchart <laurent.pinchart@...asonboard.com>; linux-
> >> phy@...ts.infradead.org
> >> Cc: Vinod Koul <vkoul@...nel.org>; linux-arm-kernel@...ts.infradead.org;
> >> linux-kernel@...r.kernel.org; Michal Simek <michal.simek@....com>;
> >> Kishon Vijay Abraham I <kishon@...nel.org>; Sean Anderson
> >> <sean.anderson@...ux.dev>
> >> Subject: [PATCH v2 4/4] phy: zynqmp: Add debugfs support
> >>
> >> Add support for printing some basic status information to debugfs. This
> >> is helpful when debugging phy consumers to make sure they are
> configuring
> >> the phy appropriately.
> >>
> >> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> >> ---
> >>
> >> Changes in v2:
> >> - Use debugfs_create_devm_seqfile
> >>
> >>  drivers/phy/xilinx/phy-zynqmp.c | 40
> >> +++++++++++++++++++++++++++++++++
> >>  1 file changed, 40 insertions(+)
> >>
> >> diff --git a/drivers/phy/xilinx/phy-zynqmp.c b/drivers/phy/xilinx/phy-
> >> zynqmp.c
> >> index b86fe2a249a8..2520c75a4a77 100644
> >> --- a/drivers/phy/xilinx/phy-zynqmp.c
> >> +++ b/drivers/phy/xilinx/phy-zynqmp.c
> >> @@ -13,6 +13,7 @@
> >>   */
> >>
> >>  #include <linux/clk.h>
> >> +#include <linux/debugfs.h>
> >>  #include <linux/delay.h>
> >>  #include <linux/io.h>
> >>  #include <linux/kernel.h>
> >> @@ -123,6 +124,15 @@
> >>  #define ICM_PROTOCOL_DP			0x4
> >>  #define ICM_PROTOCOL_SGMII		0x5
> >>
> >> +static const char *const xpsgtr_icm_str[] = {
> >> +	[ICM_PROTOCOL_PD] = "powered down",
> >
> > Protocol saying powered down seems confusing.
> > Should we say None or None(power down)?
> 
> Either works I guess. I'm just matching the define.

None seems fine - we can respin if there are no objections.
> 
> >> +	[ICM_PROTOCOL_PCIE] = "PCIe",
> >> +	[ICM_PROTOCOL_SATA] = "SATA",
> >> +	[ICM_PROTOCOL_USB] = "USB",
> >> +	[ICM_PROTOCOL_DP] = "DisplayPort",
> >> +	[ICM_PROTOCOL_SGMII] = "SGMII",
> >> +};
> >> +
> >>  /* Test Mode common reset control  parameters */
> >>  #define TM_CMN_RST			0x10018
> >>  #define TM_CMN_RST_EN			0x1
> >> @@ -788,6 +798,34 @@ static struct phy *xpsgtr_xlate(struct device *dev,
> >>  	return ERR_PTR(-EINVAL);
> >>  }
> >>
> >> +/*
> >> + * DebugFS
> >> + */
> >> +
> >> +static int xpsgtr_status_read(struct seq_file *seq, void *data)
> >> +{
> >> +	struct device *dev = seq->private;
> >> +	struct xpsgtr_phy *gtr_phy = dev_get_drvdata(dev);
> >> +	struct clk *clk;
> >> +	u32 pll_status;
> >> +
> >> +	mutex_lock(&gtr_phy->phy->mutex);
> >
> > Do we see any need for this lock? This function simply read hw register
> > /phy members and decodes it.
> 
> It's to protect against modifications to gtr_phy->refclk and ->instance.

Refclock and instance is assigned in xlate which is not protected by any
Lock.  Also xpsgtr_phy_init () uses a different gtr_mutex. So want
to understand this phy->mutex need.

> 
> These are accessed under lock elsewhere; this is not a fast path and I don't
> want to have to reason about the semantics when using a mutex is definitely
> correct.
> 
> --Sean
> 
> >> +	pll_status = xpsgtr_read_phy(gtr_phy, L0_PLL_STATUS_READ_1);
> >> +	clk = gtr_phy->dev->clk[gtr_phy->refclk];
> >> +
> >> +	seq_printf(seq, "Lane:            %u\n", gtr_phy->lane);
> >> +	seq_printf(seq, "Protocol:        %s\n",
> >> +		   xpsgtr_icm_str[gtr_phy->protocol]);
> >> +	seq_printf(seq, "Instance:        %u\n", gtr_phy->instance);
> >> +	seq_printf(seq, "Reference clock: %u (%pC)\n", gtr_phy->refclk, clk);
> >> +	seq_printf(seq, "Reference rate:  %lu\n", clk_get_rate(clk));
> >> +	seq_printf(seq, "PLL locked:      %s\n",
> >> +		   pll_status & PLL_STATUS_LOCKED ? "yes" : "no");
> >> +
> >> +	mutex_unlock(&gtr_phy->phy->mutex);
> >> +	return 0;
> >> +}
> >> +
> >>  /*
> >>   * Power Management
> >>   */
> >> @@ -937,6 +975,8 @@ static int xpsgtr_probe(struct platform_device
> *pdev)
> >>
> >>  		gtr_phy->phy = phy;
> >>  		phy_set_drvdata(phy, gtr_phy);
> >> +		debugfs_create_devm_seqfile(&phy->dev, "status", phy-
> >> >debugfs,
> >> +					    xpsgtr_status_read);
> >>  	}
> >>
> >>  	/* Register the PHY provider. */
> >> --
> >> 2.35.1.1320.gc452695387.dirty
> >