Re: [PATCH v2 3/7] firmware: raspberrypi: Provide a helper to query a clock max rate

[Stefan Wahren]

Hi Maxime,

Am 20.09.22 um 14:50 schrieb Maxime Ripard:
The firmware allows to query for its clocks the operating range of a
given clock. We'll need this for some drivers (KMS, in particular) to
infer the state of some configuration options, so let's create a
function to do so.
Signed-off-by: Maxime Ripard <max...@cerno.tech>

diff --git a/drivers/firmware/raspberrypi.c b/drivers/firmware/raspberrypi.c
index b916e1e171f8..c4b9ea70f5a7 100644
--- a/drivers/firmware/raspberrypi.c
+++ b/drivers/firmware/raspberrypi.c
@@ -228,6 +228,21 @@ static void rpi_register_clk_driver(struct device *dev)
                                                -1, NULL, 0);
  }
  
+unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw, unsigned int id)
+{
+       struct rpi_firmware_clk_rate_request msg =
+               RPI_FIRMWARE_CLK_RATE_REQUEST(id);
+       int ret;
+
+       ret = rpi_firmware_property(fw, RPI_FIRMWARE_GET_MAX_CLOCK_RATE,
+                                   &msg, sizeof(msg));
+       if (ret)
+               return 0;
+
+       return le32_to_cpu(msg.rate);
+}
+EXPORT_SYMBOL_GPL(rpi_firmware_clk_get_max_rate);
+
  static void rpi_firmware_delete(struct kref *kref)
  {
        struct rpi_firmware *fw = container_of(kref, struct rpi_firmware,
diff --git a/include/soc/bcm2835/raspberrypi-firmware.h 
b/include/soc/bcm2835/raspberrypi-firmware.h
index 74c7bcc1ac2a..10248c370229 100644
--- a/include/soc/bcm2835/raspberrypi-firmware.h
+++ b/include/soc/bcm2835/raspberrypi-firmware.h
@@ -154,12 +154,32 @@ enum rpi_firmware_clk_id {
        RPI_FIRMWARE_NUM_CLK_ID,
  };
  
+/**
+ * struct rpi_firmware_clk_rate_request - Firmware Request for a rate
+ * @id:        ID of the clock being queried
+ * @rate: Rate in Hertz. Set by the firmware.
+ *
+ * Used by @RPI_FIRMWARE_GET_CLOCK_RATE, @RPI_FIRMWARE_GET_CLOCK_MEASURED,
+ * @RPI_FIRMWARE_GET_MAX_CLOCK_RATE and @RPI_FIRMWARE_GET_MIN_CLOCK_RATE.
+ */
+struct rpi_firmware_clk_rate_request {
+       __le32 id;
+       __le32 rate;
+} __packed;
+
+#define RPI_FIRMWARE_CLK_RATE_REQUEST(_id)     \
+       {                                       \
+               .id = _id,                      \
+       }
+
  #if IS_ENABLED(CONFIG_RASPBERRYPI_FIRMWARE)
  int rpi_firmware_property(struct rpi_firmware *fw,
                          u32 tag, void *data, size_t len);
  int rpi_firmware_property_list(struct rpi_firmware *fw,
                               void *data, size_t tag_size);
  void rpi_firmware_put(struct rpi_firmware *fw);
+unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw,
+                                          unsigned int id);
  struct device_node *rpi_firmware_find_node(void);
  struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
  struct rpi_firmware *devm_rpi_firmware_get(struct device *dev,
@@ -179,6 +199,12 @@ static inline int rpi_firmware_property_list(struct 
rpi_firmware *fw,
  
  static inline void rpi_firmware_put(struct rpi_firmware *fw) { }
  
+static inline unsigned int rpi_firmware_clk_get_max_rate(struct rpi_firmware *fw,
+                                                        unsigned int id)
+{
+       return UINT_MAX;
In case the driver is disabled the function return UINT_MAX, but in case 
the firmware doesn't support RPI_FIRMWARE_GET_MAX_CLOCK_RATE it returns 
0. This looks a little bit inconsistent to me.
+}
+
  static inline struct device_node *rpi_firmware_find_node(void)
  {
        return NULL;