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Date: Tue, 20 Jan 2015 16:52:11 +0200
From: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To: Rob Herring <robherring2@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Grant Likely <grant.likely@...retlab.ca>,
Randy Dunlap <rdunlap@...radead.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: Custom printk format specifier for device node
Hi Rob,
> On Jan 20, 2015, at 16:47 , Rob Herring <robherring2@...il.com> wrote:
>
> On Tue, Jan 20, 2015 at 8:34 AM, Pantelis Antoniou
> <pantelis.antoniou@...sulko.com> wrote:
>> 90% of the usage of device node's full_name is printing it out
>> in a kernel message. Preparing for the eventual delayed allocation
>> introduce a custom printk format specifier that is both more
>> compact and more pleasant to the eye.
>
> What a great idea. ;)
>
It was a stroke of genius I tell you… :)
>> For instance typical use is:
>> pr_info("Frobbing node %s\n", node->full_name);
>>
>> Which can be written now as:
>> pr_info("Frobbing node %pO\n", node);
>>
>> A verbose format specifier (1-2) can be used to print extra
>> information about the node like its phandle and node flags.
>>
>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>> ---
>> Documentation/printk-formats.txt | 18 +++++++++++
>> lib/vsprintf.c | 67 ++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 85 insertions(+)
>>
>> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
>> index 5a615c1..6ad199f 100644
>> --- a/Documentation/printk-formats.txt
>> +++ b/Documentation/printk-formats.txt
>> @@ -231,6 +231,24 @@ struct va_format:
>> Do not use this feature without some mechanism to verify the
>> correctness of the format string and va_list arguments.
>>
>> +Device tree nodes:
>> +
>> + %pO{,1,2}
>
> 'O' is not very obvious, but I imagine we are somewhat limted in our
> choice here?
>
All the good women are married, all the handsome men are gay, all the obvious
format specifiers are taken.
>> +
>> + For printing device tree nodes. The (optional) number is the verbosity
>> + level.
>> +
>> + Examples:
>> +
>> + %pO /foo/bar@0 - Node full name
>> + %pO0 /foo/bar@0 - Same as above
>> + %pO1 /foo/bar@0[10] - Node full name + phandle
>> + %pO2 /foo/bar@0[10:DdPB] - Node full name + phandle + node flags
>> + D - dynamic
>> + d - detached
>> + P - Populated
>> + B - Populated bus
>
> We should think about what else we want to print for a node. Perhaps
> 'On' for name, 'Oc' for compatible, etc.
>
The verbosity argument is something simple that works, but I take requests...
>> +
>> u64 SHOULD be printed with %llu/%llx:
>>
>> printk("%llu", u64_var);
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
>> index ec337f6..72896cc 100644
>> --- a/lib/vsprintf.c
>> +++ b/lib/vsprintf.c
>> @@ -29,6 +29,7 @@
>> #include <linux/dcache.h>
>> #include <linux/cred.h>
>> #include <net/addrconf.h>
>> +#include <linux/of.h>
>>
>> #include <asm/page.h> /* for PAGE_SIZE */
>> #include <asm/sections.h> /* for dereference_function_descriptor() */
>> @@ -1240,6 +1241,68 @@ char *address_val(char *buf, char *end, const void *addr,
>> return number(buf, end, num, spec);
>> }
>>
>> +#if IS_ENABLED(CONFIG_OF)
>
> You can move this into the function:
>
> if (!IS_ENABLED(CONFIG_OF)
> return NULL;
>
> Looks like you'll need the patch for empty of_node_check_flag as well.
>
Yes, I tried to avoid that.
>> +static noinline_for_stack
>> +char *device_node_string(char *buf, char *end, struct device_node *dn,
>> + struct printf_spec spec, const char *fmt)
>> +{
>> + char tbuf[sizeof("[xxxxxxxxxx:xxxx]") + 1];
>> + const char *full_name;
>> + int verbosity, len, flen, i;
>> +
>> + if ((unsigned long)dn < PAGE_SIZE)
>> + return string(buf, end, "(null)", spec);
>> +
>> + full_name = of_node_full_name(dn);
>> + verbosity = 0;
>> + if (fmt[1] >= '0' && fmt[1] <= '2')
>> + verbosity = fmt[1] - '0';
>> +
>> + /* fast and simple case */
>> + switch (verbosity) {
>> + default:
>> + case 0:
>> + tbuf[0] = '\0';
>> + break;
>> + case 1:
>> + snprintf(tbuf, sizeof(tbuf), "[%u]",
>> + (u32)dn->phandle);
>> + break;
>> + case 2:
>> + snprintf(tbuf, sizeof(tbuf), "[%u:%c%c%c%c]",
>> + (u32)dn->phandle,
>> + of_node_check_flag(dn, OF_DYNAMIC) ? 'D' : '-',
>> + of_node_check_flag(dn, OF_DETACHED) ? 'd' : '-',
>> + of_node_check_flag(dn, OF_POPULATED) ? 'P' : '-',
>> + of_node_check_flag(dn, OF_POPULATED_BUS) ? 'B' : '-');
>> + break;
>> + }
>> + flen = strlen(full_name);
>> + len = flen + strlen(tbuf);
>> + if (spec.precision > 0 && len > spec.precision)
>> + len = spec.precision;
>> +
>> + if (!(spec.flags & LEFT)) {
>> + while (len < spec.field_width--) {
>> + if (buf < end)
>> + *buf = ' ';
>> + ++buf;
>> + }
>> + }
>> + for (i = 0; i < len; ++i) {
>> + if (buf < end)
>> + *buf = i < flen ? full_name[i] : tbuf[i - flen];
>> + ++buf;
>> + }
>> + while (len < spec.field_width--) {
>> + if (buf < end)
>> + *buf = ' ';
>> + ++buf;
>> + }
>> + return buf;
>> +}
>> +#endif
>> +
>> int kptr_restrict __read_mostly;
>>
>> /*
>> @@ -1459,6 +1522,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>> return dentry_name(buf, end,
>> ((const struct file *)ptr)->f_path.dentry,
>> spec, fmt);
>> +#if IS_ENABLED(CONFIG_OF)
>
> With the above, then this ifdef should not be needed.
>
Yes
>> + case 'O':
>> + return device_node_string(buf, end, ptr, spec, fmt);
>> +#endif
>> }
>> spec.flags |= SMALL;
>> if (spec.field_width == -1) {
>> --
>> 1.7.12
>>
OK, I’ll prepare the empty flag accessors patch and I’ll repost with the requested changes.
Regards
— Pantelis
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