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

Adds a function that reads from the shared buffer into memory
provided by the client.

Adds a function that writes from client memory into the shared
buffer.

Signed-off-by: Adam Young <redacted>
---
  drivers/mailbox/pcc.c | 86 +++++++++++++++++++++++++++++++++++++++++++
  include/acpi/pcc.h    | 22 +++++++++++
  2 files changed, 108 insertions(+)

diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index 22e70af1ae5d..a8b377a64e05 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c

@@ -419,6 +419,92 @@ void pcc_mbox_free_channel(struct pcc_mbox_chan *pchan)
  }
  EXPORT_SYMBOL_GPL(pcc_mbox_free_channel);
  
+/**
+ * pcc_mbox_query_bytes_available - count of bytes cwreadable in the shared buffer
+ *
+ * @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 acpi_pcct_ext_pcc_shared_memory 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 acpi_pcct_ext_pcc_shared_memory *pcc_header = data;
+	/*
+	 * The PCC header length includes the command field
+	 * but not the other values from the header.
+	 */
+	pcc_header->length = len - sizeof(struct acpi_pcct_ext_pcc_shared_memory) + sizeof(u32);
+
+	if (len > pchan->shmem_size)
+		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..9be1ae358056 100644
--- a/include/acpi/pcc.h
+++ b/include/acpi/pcc.h

@@ -37,6 +37,14 @@ 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);
+
  #else
  static inline struct pcc_mbox_chan *
  pcc_mbox_request_channel(struct mbox_client *cl, int subspace_id)

@@ -44,6 +52,20 @@ 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;
+}
  #endif
  
  #endif /* _PCC_H */