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

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Date: Thu, 13 Jun 2024 11:02:15 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
 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

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.

>> +	[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.

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
>