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Message-ID: <701000c2-11c1-4690-8d6e-0ac79572cea5@oss.qualcomm.com>
Date: Fri, 9 Jan 2026 11:15:03 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Neil Armstrong <neil.armstrong@...aro.org>,
Konrad Dybcio <konradybcio@...nel.org>,
Bjorn Andersson <andersson@...nel.org>, Kees Cook <kees@...nel.org>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Rob Clark <robin.clark@....qualcomm.com>, Sean Paul <sean@...rly.run>,
Akhil P Oommen <akhilpo@....qualcomm.com>,
Dmitry Baryshkov <lumag@...nel.org>,
Abhinav Kumar
<abhinav.kumar@...ux.dev>,
Jessica Zhang <jesszhan0024@...il.com>,
Marijn Suijten <marijn.suijten@...ainline.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-hardening@...r.kernel.org, dri-devel@...ts.freedesktop.org,
freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v3 0/3] Retrieve information about DDR from SMEM
On 1/9/26 9:20 AM, Neil Armstrong wrote:
> Hi,
>
> On 1/8/26 15:21, Konrad Dybcio wrote:
>> SMEM allows the OS to retrieve information about the DDR memory.
>> Among that information, is a semi-magic value called 'HBB', or Highest
>> Bank address Bit, which multimedia drivers (for hardware like Adreno
>> and MDSS) must retrieve in order to program the IP blocks correctly.
>>
>> This series introduces an API to retrieve that value, uses it in the
>> aforementioned programming sequences and exposes available DDR
>> frequencies in debugfs (to e.g. pass to aoss_qmp debugfs). More
>> information can be exposed in the future, as needed.
>>
>> Patch 3 should really be merged after 1&2
>
>
> While trying it, I got the following warning:
>
> In function ‘smem_dram_parse_v3_data’,
> inlined from ‘smem_dram_parse’ at drivers/soc/qcom/smem_dramc.c:380:3:
> drivers/soc/qcom/smem_dramc.c:216:31: warning: iteration 13 invokes undefined behavior [-Waggressive-loop-optimizations]
> 216 | if (freq_entry->freq_khz && freq_entry->enabled)
> | ~~~~~~~~~~^~~~~~~~~~
> drivers/soc/qcom/smem_dramc.c:213:27: note: within this loop
> 213 | for (int i = 0; i < num_freq_entries; i++) {
> | ~~^~~~~~~~~~~~~~~~~~
clang didn't seem to care..
A (really grumpy) solution would be to add:
diff --git a/drivers/soc/qcom/smem_dramc.c b/drivers/soc/qcom/smem_dramc.c
index 017bb894a91b..dc2cd7e13b88 100644
--- a/drivers/soc/qcom/smem_dramc.c
+++ b/drivers/soc/qcom/smem_dramc.c
@@ -78,7 +78,7 @@ struct ddr_freq_table {
/* V3 */
struct ddr_freq_plan_v3 {
- struct ddr_freq_table ddr_freq[MAX_DDR_FREQ_NUM_V3]; /* NOTE: some have 14 like v5 */
+ struct ddr_freq_table ddr_freq[MAX_DDR_FREQ_NUM_V3];
u8 num_ddr_freqs;
phys_addr_t clk_period_address;
};
@@ -91,6 +91,21 @@ struct ddr_details_v3 {
u8 num_channels;
};
+/* Some V3 structs have an additional frequency level */
+struct ddr_freq_plan_v3_14freqs {
+ struct ddr_freq_table ddr_freq[MAX_DDR_FREQ_NUM_V3 + 1];
+ u8 num_ddr_freqs;
+ phys_addr_t clk_period_address;
+};
+
+struct ddr_details_v3_14freqs {
+ u8 manufacturer_id;
+ u8 device_type;
+ struct ddr_part_details ddr_params[MAX_CHAN_NUM];
+ struct ddr_freq_plan_v3_14freqs ddr_freq_tbl;
+ u8 num_channels;
+};
+
/* V4 */
struct ddr_details_v4 {
u8 manufacturer_id;
@@ -201,16 +216,11 @@ int qcom_smem_dram_get_hbb(void)
}
EXPORT_SYMBOL_GPL(qcom_smem_dram_get_hbb);
-static void smem_dram_parse_v3_data(struct smem_dram *dram, void *data, bool additional_freq_entry)
+static void smem_dram_parse_v3_data(struct smem_dram *dram, void *data)
{
- /* This may be 13 or 14 */
- int num_freq_entries = MAX_DDR_FREQ_NUM_V3;
struct ddr_details_v3 *details = data;
- if (additional_freq_entry)
- num_freq_entries++;
-
- for (int i = 0; i < num_freq_entries; i++) {
+ for (int i = 0; i < MAX_DDR_FREQ_NUM_V3; i++) {
struct ddr_freq_table *freq_entry = &details->ddr_freq_tbl.ddr_freq[i];
if (freq_entry->freq_khz && freq_entry->enabled)
@@ -218,6 +228,18 @@ static void smem_dram_parse_v3_data(struct smem_dram *dram, void *data, bool add
}
}
+static void smem_dram_parse_v3_14freqs_data(struct smem_dram *dram, void *data)
+{
+ struct ddr_details_v3_14freqs *details = data;
+
+ for (int i = 0; i < MAX_DDR_FREQ_NUM_V3 + 1; i++) {
+ struct ddr_freq_table *freq_entry = &details->ddr_freq_tbl.ddr_freq[i];
+
+ if (freq_entry->freq_khz && freq_entry->enabled)
+ dram->frequencies[dram->num_frequencies++] = 1000 * freq_entry->freq_khz;
+ }
+}
+
static void smem_dram_parse_v4_data(struct smem_dram *dram, void *data)
{
struct ddr_details_v4 *details = data;
@@ -273,8 +295,7 @@ static int smem_dram_infer_struct_version(size_t size)
if (size == sizeof(struct ddr_details_v3))
return INFO_V3;
- if (size == sizeof(struct ddr_details_v3)
- + sizeof(struct ddr_freq_table))
+ if (size == sizeof(struct ddr_details_v3_14freqs))
return INFO_V3_WITH_14_FREQS;
if (size == sizeof(struct ddr_details_v4))
@@ -374,10 +395,10 @@ struct dentry *smem_dram_parse(struct device *dev)
switch (ver) {
case INFO_V3:
- smem_dram_parse_v3_data(dram, data, false);
+ smem_dram_parse_v3_data(dram, data);
break;
case INFO_V3_WITH_14_FREQS:
- smem_dram_parse_v3_data(dram, data, true);
+ smem_dram_parse_v3_14freqs_data(dram, data);
break;
case INFO_V4:
smem_dram_parse_v4_data(dram, data);
A less grumpy one that I'm not sure would make the compiler happy would be:
diff --git a/drivers/soc/qcom/smem_dramc.c b/drivers/soc/qcom/smem_dramc.c
index 017bb894a91b..3653402fa70c 100644
--- a/drivers/soc/qcom/smem_dramc.c
+++ b/drivers/soc/qcom/smem_dramc.c
@@ -206,15 +206,16 @@ static void smem_dram_parse_v3_data(struct smem_dram *dram, void *data, bool add
/* This may be 13 or 14 */
int num_freq_entries = MAX_DDR_FREQ_NUM_V3;
struct ddr_details_v3 *details = data;
+ struct ddr_freq_table *freq_entry;
if (additional_freq_entry)
num_freq_entries++;
- for (int i = 0; i < num_freq_entries; i++) {
- struct ddr_freq_table *freq_entry = &details->ddr_freq_tbl.ddr_freq[i];
+ freq_entry = details->ddr_freq_tbl.ddr_freq;
+ for (int i = 0; i < num_freq_entries; i++) {
if (freq_entry->freq_khz && freq_entry->enabled)
- dram->frequencies[dram->num_frequencies++] = 1000 * freq_entry->freq_khz;
+ dram->frequencies[dram->num_frequencies++] = 1000 * (freq_entry++)->freq_khz;
}
}
WDYT?
Konrad
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