Re: [PATCH v2 3/4] firmware: qcom_scm: Refactor code to support multiple download mode

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On 3/16/2023 9:57 PM, Dmitry Baryshkov wrote:
On 03/03/2023 09:46, Mukesh Ojha wrote:
Thanks for your time in checking this..

On 3/1/2023 4:29 PM, Dmitry Baryshkov wrote:
On 01/03/2023 11:55, Mukesh Ojha wrote:
Currently on Qualcomm SoC, download_mode is enabled if
CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT is selected.

Refactor the code such that it supports multiple download
modes and drop CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT config
instead, give interface to set the download mode from
module parameter.

Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
---
Changes in v2:
  - Passed download mode as parameter
  - Accept human accepatable download mode string.
  - enable = !!dload_mode
  - Shifted module param callback to somewhere down in
    the file so that it no longer need to know the
    prototype of qcom_scm_set_download_mode()
  - updated commit text.

  drivers/firmware/Kconfig    | 11 --------
  drivers/firmware/qcom_scm.c | 65 ++++++++++++++++++++++++++++++++++++++-------
  2 files changed, 56 insertions(+), 20 deletions(-)

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index b59e304..ff7e9f3 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -215,17 +215,6 @@ config MTK_ADSP_IPC
  config QCOM_SCM
      tristate
-config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
-    bool "Qualcomm download mode enabled by default"
-    depends on QCOM_SCM
-    help
-      A device with "download mode" enabled will upon an unexpected
-      warm-restart enter a special debug mode that allows the user to
-      "download" memory content over USB for offline postmortem analysis.
-      The feature can be enabled/disabled on the kernel command line.
-
-      Say Y here to enable "download mode" by default.
-
  config SYSFB
      bool
      select BOOT_VESA_SUPPORT
diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
index c9f1fad..ca07208 100644
--- a/drivers/firmware/qcom_scm.c
+++ b/drivers/firmware/qcom_scm.c
@@ -17,17 +17,22 @@
  #include <linux/clk.h>
  #include <linux/reset-controller.h>
  #include <linux/arm-smccc.h>
+#include <linux/kstrtox.h>
  #include "qcom_scm.h"
-static bool download_mode = IS_ENABLED(CONFIG_QCOM_SCM_DOWNLOAD_MODE_DEFAULT);
-module_param(download_mode, bool, 0);
-
  #define SCM_HAS_CORE_CLK    BIT(0)
  #define SCM_HAS_IFACE_CLK    BIT(1)
  #define SCM_HAS_BUS_CLK        BIT(2)
  #define QCOM_DOWNLOAD_MODE_MASK 0x30
+#define QCOM_DOWNLOAD_FULLDUMP    0x10
+#define QCOM_DOWNLOAD_NODUMP    0x0
+
+#define MAX_DLOAD_LEN    8
+
+static char download_mode[] = "off";
+static u32 dload_mode;
  struct qcom_scm {
      struct device *dev;
@@ -417,8 +422,9 @@ static int __qcom_scm_set_dload_mode(struct device *dev, bool enable)
      return qcom_scm_call_atomic(__scm->dev, &desc, NULL);
  }
-static void qcom_scm_set_download_mode(bool enable)
+static void qcom_scm_set_download_mode(u32 dload_mode)
  {
+    bool enable = !!dload_mode;
      bool avail;
      int ret = 0;
      u32 val;
@@ -438,7 +444,7 @@ static void qcom_scm_set_download_mode(bool enable)
          val &= ~QCOM_DOWNLOAD_MODE_MASK;
          if (enable)
-            val |= QCOM_SCM_BOOT_SET_DLOAD_MODE;
+            val |= dload_mode;
          ret = qcom_scm_io_writel(__scm->dload_mode_addr, val);
      } else {
@@ -1338,6 +1344,47 @@ bool qcom_scm_is_available(void)
  }
  EXPORT_SYMBOL(qcom_scm_is_available);
+static int set_dload_mode(const char *val, const struct kernel_param *kp)
+{
+    int ret;
+
+    if (!strncmp(val, "full", strlen("full"))) {
+        dload_mode = QCOM_DOWNLOAD_FULLDUMP;
+    } else if (!strncmp(val, "off", strlen("off"))) {
+        dload_mode = QCOM_DOWNLOAD_NODUMP;
+    } else {
+        if (kstrtouint(val, 0, &dload_mode) ||
+             !(dload_mode == 0 || dload_mode == 1)) {
+            pr_err("unknown download mode\n");
+            return -EINVAL;
+        }
+
+    }
+
+    ret = param_set_copystring(val, kp);
+    if (ret)
+        return ret;
+
+    if (__scm)
+        qcom_scm_set_download_mode(dload_mode);
+
+    return 0;
+}
+
+static const struct kernel_param_ops dload_mode_param_ops = {
+    .set = set_dload_mode,
+    .get = param_get_string,

Please follow the param_get_bool approach and return sanitized data here. In other words, "full" / "none" depending on the dload_mode instead of storing the passed string and returning it later.


This could be done.

+};
+
+static struct kparam_string dload_mode_param = {
+    .string = download_mode,
+    .maxlen = MAX_DLOAD_LEN,

I think writing "full" to this param might overwrite some kernel data. "00000000" should be even worse.

There is check in param_set_copystring() which would avoid that.


No. The check will validate the value's length against MAX_DLOAD_LEN. But it will not safeguard your code. download_mode's size is less than MAX_DLOAD_LEN.

Oops !! you are right..,
Will fix it in v3.

-Mukesh





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