[PATCH v30 2/3] mailbox: pcc: functions for reading and writing PCC extended data

Adam Young
2025-10-16T21:02:42Z

Adds functions that aid in compliance with the PCC protocol by
checking the command complete flag status.

Adds a function that exposes the size of the shared buffer without
activating the channel.

Adds a function that allows a client to query the number of bytes
avaialbel to read in order to preallocate buffers for reading.

Signed-off-by: Adam Young <admiyo@os.amperecomputing.com>
---
drivers/mailbox/pcc.c | 129 ++++++++++++++++++++++++++++++++++++++++++
include/acpi/pcc.h | 38 +++++++++++++
2 files changed, 167 insertions(+)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index 978a7b674946..653897d61db5 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -367,6 +367,46 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
return IRQ_HANDLED;
}

+static
+struct pcc_chan_info *lookup_channel_info(int subspace_id)
+{
+ struct pcc_chan_info *pchan;
+ struct mbox_chan *chan;
+
+ if (subspace_id < 0 || subspace_id >= pcc_chan_count)
+ return ERR_PTR(-ENOENT);
+
+ pchan = chan_info + subspace_id;
+ chan = pchan->chan.mchan;
+ if (IS_ERR(chan) || chan->cl) {
+ pr_err("Channel not found for idx: %d\n", subspace_id);
+ return ERR_PTR(-EBUSY);
+ }
+ return pchan;
+}
+
+/**
+ * pcc_mbox_buffer_size - PCC clients call this function to
+ * request the size of the shared buffer in cases
+ * where requesting the channel would prematurely
+ * trigger channel activation and message delivery.
+ * @subspace_id: The PCC Subspace index as parsed in the PCC client
+ * ACPI package. This is used to lookup the array of PCC
+ * subspaces as parsed by the PCC Mailbox controller.
+ *
+ * Return: The size of the shared buffer.
+ */
+int pcc_mbox_buffer_size(int index)
+{
+ struct pcc_chan_info *pchan = lookup_channel_info(index);
+
+ if (IS_ERR(pchan))
+ return -1;
+ return pchan->chan.shmem_size;
+}
+EXPORT_SYMBOL_GPL(pcc_mbox_buffer_size);
+
+
/**
* pcc_mbox_request_channel - PCC clients call this function to
* request a pointer to their PCC subspace, from which they
@@ -437,6 +477,95 @@ void pcc_mbox_free_channel(struct pcc_mbox_chan *pchan)
}
EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);

+/**
+ * pcc_mbox_query_bytes_available
+ *
+ * @pchan pointer to channel associated with buffer
+ * Return: the number of bytes available to read from the shared buffer
+ */
+int pcc_mbox_query_bytes_available(struct pcc_mbox_chan *pchan)
+{
+ struct pcc_extended_header pcc_header;
+ struct pcc_chan_info *pinfo = pchan->mchan->con_priv;
+ int data_len;
+ u64 val;
+
+ pcc_chan_reg_read(&pinfo->cmd_complete, &val);
+ if (val) {
+ pr_info("%s Buffer not enabled for reading", __func__);
+ return -1;
+ }
+ memcpy_fromio(&pcc_header, pchan->shmem,
+ sizeof(pcc_header));
+ data_len = pcc_header.length - sizeof(u32) + sizeof(pcc_header);
+ return data_len;
+}
+EXPORT_SYMBOL_GPL(pcc_mbox_query_bytes_available);
+
+/**
+ * pcc_mbox_read_from_buffer - Copy bytes from shared buffer into data
+ *
+ * @pchan - channel associated with the shared buffer
+ * @len - number of bytes to read
+ * @data - pointer to memory in which to write the data from the
+ * shared buffer
+ *
+ * Return: number of bytes read and written into daa
+ */
+int pcc_mbox_read_from_buffer(struct pcc_mbox_chan *pchan, int len, void *data)
+{
+ struct pcc_chan_info *pinfo = pchan->mchan->con_priv;
+ int data_len;
+ u64 val;
+
+ pcc_chan_reg_read(&pinfo->cmd_complete, &val);
+ if (val) {
+ pr_info("%s buffer not enabled for reading", __func__);
+ return -1;
+ }
+ data_len = pcc_mbox_query_bytes_available(pchan);
+ if (len < data_len)
+ data_len = len;
+ memcpy_fromio(data, pchan->shmem, len);
+ return len;
+}
+EXPORT_SYMBOL_GPL(pcc_mbox_read_from_buffer);
+
+/**
+ * pcc_mbox_write_to_buffer, copy the contents of the data
+ * pointer to the shared buffer. Confirms that the command
+ * flag has been set prior to writing. Data should be a
+ * properly formatted extended data buffer.
+ * pcc_mbox_write_to_buffer
+ * @pchan: channel
+ * @len: Length of the overall buffer passed in, including the
+ * Entire header. The length value in the shared buffer header
+ * Will be calculated from len.
+ * @data: Client specific data to be written to the shared buffer.
+ * Return: number of bytes written to the buffer.
+ */
+int pcc_mbox_write_to_buffer(struct pcc_mbox_chan *pchan, int len, void *data)
+{
+ struct pcc_extended_header *pcc_header = data;
+ struct mbox_chan *mbox_chan = pchan->mchan;
+
+ /*
+ * The PCC header length includes the command field
+ * but not the other values from the header.
+ */
+ pcc_header->length = len - sizeof(struct pcc_extended_header) + sizeof(u32);
+
+ if (!pcc_last_tx_done(mbox_chan)) {
+ pr_info("%s pchan->cmd_complete not set.", __func__);
+ return 0;
+ }
+ memcpy_toio(pchan->shmem, data, len);
+
+ return len;
+}
+EXPORT_SYMBOL_GPL(pcc_mbox_write_to_buffer);
+
+
/**
* pcc_send_data - Called from Mailbox Controller code. Used
* here only to ring the channel doorbell. The PCC client
diff --git a/include/acpi/pcc.h b/include/acpi/pcc.h
index 840bfc95bae3..96a6f85fc1ba 100644
--- a/include/acpi/pcc.h
+++ b/include/acpi/pcc.h
@@ -19,6 +19,13 @@ struct pcc_mbox_chan {
u16 min_turnaround_time;
};

+struct pcc_extended_header {
+ u32 signature;
+ u32 flags;
+ u32 length;
+ u32 command;
+};
+
/* Generic Communications Channel Shared Memory Region */
#define PCC_SIGNATURE 0x50434300
/* Generic Communications Channel Command Field */
@@ -37,6 +44,17 @@ struct pcc_mbox_chan {
extern struct pcc_mbox_chan *
pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id);
extern void pcc_mbox_free_channel(struct pcc_mbox_chan *chan);
+extern
+int pcc_mbox_write_to_buffer(struct pcc_mbox_chan *pchan, int len, void *data);
+extern
+int pcc_mbox_query_bytes_available(struct pcc_mbox_chan *pchan);
+extern
+int pcc_mbox_read_from_buffer(struct pcc_mbox_chan *pchan, int len,
+ void *data);
+extern
+int pcc_mbox_buffer_size(int index);
+
+
#else
static inline struct pcc_mbox_chan *
pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id)
@@ -44,6 +62,26 @@ pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id)
return ERR_PTR(-ENODEV);
}
static inline void pcc_mbox_free_channel(struct pcc_mbox_chan *chan) { }
+static inline
+int pcc_mbox_write_to_buffer(struct pcc_mbox_chan *pchan, int len, void *data)
+{
+ return 0;
+}
+static inline int pcc_mbox_query_bytes_available(struct pcc_mbox_chan *pchan);
+{
+ return 0;
+}
+static inline
+int pcc_mbox_read_from_buffer(struct pcc_mbox_chan *pchan, int len, void *data)
+{
+ return 0;
+}
+static inline
+int pcc_mbox_buffer_size(int index)
+{
+ return -1;
+}
+
#endif

#endif /* _PCC_H */
--
2.43.0