[alsa-devel] [RFC PATCH 04/40] soundwire: intel: add debugfs register dump

[Greg KH]

On Thu, Jul 25, 2019 at 06:39:56PM -0500, Pierre-Louis Bossart wrote:
> Add debugfs file to dump the Intel SoundWire registers
> 
> Credits: this patch is based on an earlier internal contribution by
> Vinod Koul, Sanyog Kale, Shreyas Nc and Hardik Shah. The main change
> is the use of scnprintf to avoid known issues with snprintf.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> ---
>  drivers/soundwire/intel.c | 115 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 115 insertions(+)
> 
> diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
> index 317873bc0555..aeadc341c0a3 100644
> --- a/drivers/soundwire/intel.c
> +++ b/drivers/soundwire/intel.c
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <linux/acpi.h>
> +#include <linux/debugfs.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
>  #include <linux/interrupt.h>
> @@ -16,6 +17,7 @@
>  #include <linux/soundwire/sdw.h>
>  #include <linux/soundwire/sdw_intel.h>
>  #include "cadence_master.h"
> +#include "bus.h"
>  #include "intel.h"
>  
>  /* Intel SHIM Registers Definition */
> @@ -98,6 +100,7 @@ struct sdw_intel {
>  	struct sdw_cdns cdns;
>  	int instance;
>  	struct sdw_intel_link_res *res;
> +	struct dentry *fs;
>  };
>  
>  #define cdns_to_intel(_cdns) container_of(_cdns, struct sdw_intel, cdns)
> @@ -161,6 +164,115 @@ static int intel_set_bit(void __iomem *base, int offset, u32 value, u32 mask)
>  	return -EAGAIN;
>  }
>  
> +/*
> + * debugfs
> + */
> +
> +#define RD_BUF (2 * PAGE_SIZE)
> +
> +static ssize_t intel_sprintf(void __iomem *mem, bool l,
> +			     char *buf, size_t pos, unsigned int reg)
> +{
> +	int value;
> +
> +	if (l)
> +		value = intel_readl(mem, reg);
> +	else
> +		value = intel_readw(mem, reg);
> +
> +	return scnprintf(buf + pos, RD_BUF - pos, "%4x\t%4x\n", reg, value);
> +}
> +
> +static ssize_t intel_reg_read(struct file *file, char __user *user_buf,
> +			      size_t count, loff_t *ppos)
> +{
> +	struct sdw_intel *sdw = file->private_data;
> +	void __iomem *s = sdw->res->shim;
> +	void __iomem *a = sdw->res->alh;
> +	char *buf;
> +	ssize_t ret;
> +	int i, j;
> +	unsigned int links, reg;
> +
> +	buf = kzalloc(RD_BUF, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	links = intel_readl(s, SDW_SHIM_LCAP) & GENMASK(2, 0);
> +
> +	ret = scnprintf(buf, RD_BUF, "Register  Value\n");
> +	ret += scnprintf(buf + ret, RD_BUF - ret, "\nShim\n");
> +
> +	for (i = 0; i < 4; i++) {
> +		reg = SDW_SHIM_LCAP + i * 4;
> +		ret += intel_sprintf(s, true, buf, ret, reg);
> +	}
> +
> +	for (i = 0; i < links; i++) {
> +		ret += scnprintf(buf + ret, RD_BUF - ret, "\nLink%d\n", i);
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTLSCAP(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTLS0CM(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTLS1CM(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTLS2CM(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTLS3CM(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_PCMSCAP(i));
> +
> +		for (j = 0; j < 8; j++) {
> +			ret += intel_sprintf(s, false, buf, ret,
> +					SDW_SHIM_PCMSYCHM(i, j));
> +			ret += intel_sprintf(s, false, buf, ret,
> +					SDW_SHIM_PCMSYCHC(i, j));
> +		}
> +
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_PDMSCAP(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_IOCTL(i));
> +		ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_CTMCTL(i));
> +	}
> +
> +	ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_WAKEEN);
> +	ret += intel_sprintf(s, false, buf, ret, SDW_SHIM_WAKESTS);
> +
> +	ret += scnprintf(buf + ret, RD_BUF - ret, "\nALH\n");
> +	for (i = 0; i < 8; i++)
> +		ret += intel_sprintf(a, true, buf, ret, SDW_ALH_STRMZCFG(i));
> +
> +	ret = simple_read_from_buffer(user_buf, count, ppos, buf, ret);
> +	kfree(buf);
> +
> +	return ret;
> +}
> +
> +static const struct file_operations intel_reg_fops = {
> +	.open = simple_open,
> +	.read = intel_reg_read,
> +	.llseek = default_llseek,
> +};

DEFINE_SIMPLE_ATTRIBUTE()?

> +
> +static void intel_debugfs_init(struct sdw_intel *sdw)
> +{
> +	struct dentry *root = sdw->cdns.bus.debugfs;
> +
> +	if (!root)
> +		return;
> +
> +	sdw->fs = debugfs_create_dir("intel-sdw", root);
> +	if (IS_ERR_OR_NULL(sdw->fs)) {
> +		dev_err(sdw->cdns.dev, "debugfs root creation failed\n");

No, come on, don't do that.  I've been sweeping the kernel tree to
remove this anti-pattern.

The debugfs core will print an error if you got something wrong, just
call the function and move on, you NEVER need to check the return value
of a debugfs call.

thanks,

greg k-h