Re: [PATCH 04/13] drm/xe/guc: Add string KLV encoding helper

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

On 7/3/2026 3:29 PM, Michał Winiarski wrote:
> On Tue, Jun 30, 2026 at 03:26:23PM +0200, Michal Wajdeczko wrote:
>> We also plan to encode a text data as KLV. Add helper for that too.
>>
>> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
>> ---
>>  drivers/gpu/drm/xe/xe_guc_klv_helpers.c | 31 +++++++++++++++++++++++++
>>  drivers/gpu/drm/xe/xe_guc_klv_helpers.h |  1 +
>>  2 files changed, 32 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_guc_klv_helpers.c b/drivers/gpu/drm/xe/xe_guc_klv_helpers.c
>> index e84d1f5f5c56..a5fcfc4a6c37 100644
>> --- a/drivers/gpu/drm/xe/xe_guc_klv_helpers.c
>> +++ b/drivers/gpu/drm/xe/xe_guc_klv_helpers.c
>> @@ -188,6 +188,11 @@ int xe_guc_klv_count(const u32 *klvs, u32 num_dwords)
>>  	return num_dwords ? -ENODATA : num_klvs;
>>  }
>>  
>> +static size_t to_num_bytes(u16 dwords)
>> +{
>> +	return dwords * sizeof(u32);
>> +}
>> +
>>  static u16 to_num_dwords(size_t size)
>>  {
>>  	return round_up(size, sizeof(u32)) / sizeof(u32);
>> @@ -243,3 +248,29 @@ u32 *xe_guc_klv_encode_u64(u32 *klvs, u32 avail, u16 key, u64 value)
>>  	*klvs++ = upper_32_bits(value);
>>  	return klvs;
>>  }
>> +
>> +/**
>> + * xe_guc_klv_encode_string() - Encode string as KLV.
>> + * @klvs: the buffer where to place KLV
>> + * @avail: number of dwords (u32) available in the buffer
>> + * @key: key to be used
>> + * @s: string to be encoded
>> + *
>> + * Return: pointer to the buffer location past the encoded KLV or
>> + *         an ERR_PTR if there was no space to encode the KLV.
>> + */
>> +u32 *xe_guc_klv_encode_string(u32 *klvs, u32 avail, u16 key, const char *s)
>> +{
>> +	size_t size = strnlen(s, FIELD_MAX(GUC_KLV_0_LEN) - 1) + 1; /* \0 */
> 
> We're mixing up units (dwords / bytes) here.

oops, it supposed to be to_num_bytes()

> Also - should we error out if the string would get truncated?

it's a good idea

> 
> Thanks,
> -Michał
> 
>> +	u16 len = to_num_dwords(size);
>> +
>> +	if (IS_ERR(klvs))
>> +		return klvs;
>> +
>> +	if (avail < GUC_KLV_LEN_MIN + len)
>> +		return ERR_PTR(-ENOSPC);
>> +
>> +	*klvs++ = PREP_GUC_KLV(key, len);
>> +	strscpy_pad((void *)klvs, s, to_num_bytes(len));
>> +	return klvs + len;
>> +}
>> diff --git a/drivers/gpu/drm/xe/xe_guc_klv_helpers.h b/drivers/gpu/drm/xe/xe_guc_klv_helpers.h
>> index 713ef7f7b9f2..1c576456efc5 100644
>> --- a/drivers/gpu/drm/xe/xe_guc_klv_helpers.h
>> +++ b/drivers/gpu/drm/xe/xe_guc_klv_helpers.h
>> @@ -19,6 +19,7 @@ int xe_guc_klv_count(const u32 *klvs, u32 num_dwords);
>>  
>>  u32 *xe_guc_klv_encode_u32(u32 *klvs, u32 avail, u16 key, u32 value);
>>  u32 *xe_guc_klv_encode_u64(u32 *klvs, u32 avail, u16 key, u64 value);
>> +u32 *xe_guc_klv_encode_string(u32 *klvs, u32 avail, u16 key, const char *s);
>>  
>>  /**
>>   * PREP_GUC_KLV - Prepare KLV header value based on provided key and len.
>> -- 
>> 2.47.1
>>