[PATCH v2 3/7] hw/i2c: pmbus: Page #255 is valid page for read requests.

[Jae Hyun Yoo]

From: Maheswara Kurapati <quic_mkurapat@quicinc.com>

Current implementation of the pmbus core driver treats the read request
for page 255 as invalid request and sets the invalid command bit (bit 7)
in the STATUS_CML register. As per the PMBus specification it is a valid
request.

Refer to the PMBus specification, revision 1.3.1, section 11.10 PAGE,
on the page 58:
  "Setting the PAGE to FFh means that all subsequent comands are to be
   applied to all outputs.

   Some commands, such as READ_TEMPERATURE, may use a common sensor but
   be available on all pages of a device. Such implementations are the
   decision of each device manufacturer or are specified in a PMBus
   Application Profile. Consult the manufacturer's documents or the
   Application Profile Specification as needed."

For e.g.,
The VOUT_MODE is a valid command for page 255 for maxim 31785 device.
refer to Table 1. PMBus Command Codes on page 14 in the datasheet.
https://datasheets.maximintegrated.com/en/ds/MAX31785.pdf

Fixes: 38870253f1d1 ("hw/i2c: pmbus: fix error returns and guard against out of 
range accesses")

Signed-off-by: Maheswara Kurapati <quic_mkurapat@quicinc.com>
Signed-off-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Reviewed-by: Titus Rwantare <titusr@google.com>
---
Changes in v2:
* Fixed comment for a case of PB_ALL_PAGES. (Titus)
* Removed an error log printing when it handles PB_ALL_PAGES. (Jae)

 hw/i2c/pmbus_device.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/hw/i2c/pmbus_device.c b/hw/i2c/pmbus_device.c
index 62885fa6a15e..749a33af827b 100644
--- a/hw/i2c/pmbus_device.c
+++ b/hw/i2c/pmbus_device.c
@@ -284,14 +284,10 @@ static uint8_t pmbus_receive_byte(SMBusDevice *smd)
 
     /*
      * Reading from all pages will return the value from page 0,
-     * this is unspecified behaviour in general.
+     * means that all subsequent commands are to be applied to all output.
      */
     if (pmdev->page == PB_ALL_PAGES) {
         index = 0;
-        qemu_log_mask(LOG_GUEST_ERROR,
-                      "%s: tried to read from all pages\n",
-                      __func__);
-        pmbus_cml_error(pmdev);
     } else if (pmdev->page > pmdev->num_pages - 1) {
         qemu_log_mask(LOG_GUEST_ERROR,
                       "%s: page %d is out of range\n",
-- 
2.25.1