Re: [PATCH] drm/i915/dp: use seq buf for printing rates

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 27 Nov 2024, Gustavo Sousa <gustavo.sousa@intel.com> wrote:
> Quoting Jani Nikula (2024-11-27 10:18:38-03:00)
>>Hand rolling the buffer overflow handling with snprintf() is a bit
>>tedious. The seq_buf interface is made for this. Switch to it.
>
> Cool! Today I learned a new kernel interface. :-)

\o/

>>
>>Use struct intel_display while at it.
>>
>>Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>>---
>> drivers/gpu/drm/i915/display/intel_dp.c | 36 ++++++++++---------------
>> 1 file changed, 14 insertions(+), 22 deletions(-)
>>
>>diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>>index 053a9a4182e7..4471c8fcd478 100644
>>--- a/drivers/gpu/drm/i915/display/intel_dp.c
>>+++ b/drivers/gpu/drm/i915/display/intel_dp.c
>>@@ -28,6 +28,7 @@
>> #include <linux/export.h>
>> #include <linux/i2c.h>
>> #include <linux/notifier.h>
>>+#include <linux/seq_buf.h>
>> #include <linux/slab.h>
>> #include <linux/sort.h>
>> #include <linux/string_helpers.h>
>>@@ -1506,41 +1507,32 @@ bool intel_dp_source_supports_tps4(struct drm_i915_private *i915)
>>         return DISPLAY_VER(i915) >= 10;
>> }
>> 
>>-static void snprintf_int_array(char *str, size_t len,
>>-                               const int *array, int nelem)
>>+static void seq_buf_print_array(struct seq_buf *s, const int *array, int nelem)
>> {
>>         int i;
>> 
>>-        str[0] = '\0';
>>-
>>-        for (i = 0; i < nelem; i++) {
>>-                int r = snprintf(str, len, "%s%d", i ? ", " : "", array[i]);
>>-                if (r >= len)
>>-                        return;
>>-                str += r;
>>-                len -= r;
>>-        }
>>+        for (i = 0; i < nelem; i++)
>>+                seq_buf_printf(s, "%s%d", i ? ", " : "", array[i]);
>> }
>> 
>> static void intel_dp_print_rates(struct intel_dp *intel_dp)
>> {
>>-        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>>-        char str[128]; /* FIXME: too big for stack? */
>>+        struct intel_display *display = to_intel_display(intel_dp);
>>+        DECLARE_SEQ_BUF(s, 128); /* FIXME: too big for stack? */
>
> I wonder if just using drm_dbg_printer() would make things simpler,
> without requiring a buffer.

Mmh, that's always line based, isn't it? It would result in each rate
getting printed on its own line, which is too spammy.

> Anyway, the patch looks good to me, so:
>
> Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>

Thanks!

>
>> 
>>         if (!drm_debug_enabled(DRM_UT_KMS))
>>                 return;
>> 
>>-        snprintf_int_array(str, sizeof(str),
>>-                           intel_dp->source_rates, intel_dp->num_source_rates);
>>-        drm_dbg_kms(&i915->drm, "source rates: %s\n", str);
>>+        seq_buf_print_array(&s, intel_dp->source_rates, intel_dp->num_source_rates);
>>+        drm_dbg_kms(display->drm, "source rates: %s\n", seq_buf_str(&s));
>> 
>>-        snprintf_int_array(str, sizeof(str),
>>-                           intel_dp->sink_rates, intel_dp->num_sink_rates);
>>-        drm_dbg_kms(&i915->drm, "sink rates: %s\n", str);
>>+        seq_buf_clear(&s);
>>+        seq_buf_print_array(&s, intel_dp->sink_rates, intel_dp->num_sink_rates);
>>+        drm_dbg_kms(display->drm, "sink rates: %s\n", seq_buf_str(&s));
>> 
>>-        snprintf_int_array(str, sizeof(str),
>>-                           intel_dp->common_rates, intel_dp->num_common_rates);
>>-        drm_dbg_kms(&i915->drm, "common rates: %s\n", str);
>>+        seq_buf_clear(&s);
>>+        seq_buf_print_array(&s, intel_dp->common_rates, intel_dp->num_common_rates);
>>+        drm_dbg_kms(display->drm, "common rates: %s\n", seq_buf_str(&s));
>> }
>> 
>> static int forced_link_rate(struct intel_dp *intel_dp)
>>-- 
>>2.39.5
>>

-- 
Jani Nikula, Intel