Re: [PATCH v10 03/12] peci: Add support for PECI bus driver core

[Joel Stanley]

Hello Jae,

On Tue, 8 Jan 2019 at 08:11, Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx> wrote:
>
> This commit adds driver implementation for PECI bus core into linux
> driver framework.

I would like to help you get this merged next release cycle, as we are
now carrying it in OpenBMC. I suggest we ask Greg to queue it up if
there are no objections after you've addressed my questions.

> +static u8 peci_aw_fcs(u8 *data, int len)

I was wondering what aw_fcs meant. I notice that later on you describe
it as an Assure Write Frame Check Sequence byte. You could add a
comment next to this function :)

Instead of casing to u8 every time you call this, you could have this
take a struct peci_xfer_msg * and cast when calling crc8.

> +{
> +       return crc8(peci_crc8_table, data, (size_t)len, 0);
> +}
> +
> +static int __peci_xfer(struct peci_adapter *adapter, struct peci_xfer_msg *msg,
> +                      bool do_retry, bool has_aw_fcs)
> +{
> +       ktime_t start, end;
> +       s64 elapsed_ms;
> +       int rc = 0;
> +
> +       /**

These are for kerneldoc, and the comments aren't kerneldoc. Replace
them with /* instead.

> +        * For some commands, the PECI originator may need to retry a command if
> +        * the processor PECI client responds with a 0x8x completion code. In
> +        * each instance, the processor PECI client may have started the
> +        * operation but not completed it yet. When the 'retry' bit is set, the
> +        * PECI client will ignore a new request if it exactly matches a
> +        * previous valid request.
> +        */
> +
> +       if (do_retry)
> +               start = ktime_get();
> +
> +       do {
> +               rc = adapter->xfer(adapter, msg);
> +
> +               if (!do_retry || rc)
> +                       break;
> +
> +               if (msg->rx_buf[0] == DEV_PECI_CC_SUCCESS)
> +                       break;
> +
> +               /* Retry is needed when completion code is 0x8x */
> +               if ((msg->rx_buf[0] & DEV_PECI_CC_RETRY_CHECK_MASK) !=
> +                   DEV_PECI_CC_NEED_RETRY) {
> +                       rc = -EIO;
> +                       break;
> +               }
> +
> +               /* Set the retry bit to indicate a retry attempt */
> +               msg->tx_buf[1] |= DEV_PECI_RETRY_BIT;
> +
> +               /* Recalculate the AW FCS if it has one */
> +               if (has_aw_fcs)
> +                       msg->tx_buf[msg->tx_len - 1] = 0x80 ^

Can we guarantee that msg->tx_len will be set to non-zero whenever has_aw_fcs?

I suggest checking before doing the assignment in case a new caller is
added and they make a mistake.

> +static int peci_ioctl_get_dib(struct peci_adapter *adapter, void *vmsg)
> +{
> +       struct peci_get_dib_msg *umsg = vmsg;
> +       struct peci_xfer_msg msg;
> +       int rc;
> +
> +       msg.addr      = umsg->addr;
> +       msg.tx_len    = GET_DIB_WR_LEN;
> +       msg.rx_len    = GET_DIB_RD_LEN;
> +       msg.tx_buf[0] = GET_DIB_PECI_CMD;
> +
> +       rc = peci_xfer(adapter, &msg);

Most of tx_buf is going to be uninitialised. I assume a well behaving
adapter->xfer will check this and only send the correct number of
bytes, but it might pay to zero out struct peci_xfer_msg in all of
these functions?

> +       if (rc)
> +               return rc;
> +
> +       umsg->dib = le64_to_cpup((__le64 *)msg.rx_buf);
> +
> +       return 0;
> +}

> +
> +#if IS_ENABLED(CONFIG_OF)
> +static struct peci_client *peci_of_register_device(struct peci_adapter *adapter,
> +                                                  struct device_node *node)
> +{
> +       struct peci_board_info info = {};
> +       struct peci_client *result;
> +       const __be32 *addr_be;
> +       int len;
> +
> +       dev_dbg(&adapter->dev, "register %pOF\n", node);
> +
> +       if (of_modalias_node(node, info.type, sizeof(info.type)) < 0) {

I don't understand why you're doing this. Won't this always be peci,
as your binding requires?

> +               dev_err(&adapter->dev, "modalias failure on %pOF\n", node);
> +               return ERR_PTR(-EINVAL);
> +       }
> +
> +       addr_be = of_get_property(node, "reg", &len);
> +       if (!addr_be || len < sizeof(*addr_be)) {

The second check looks suspicious.

You could fix it to check the expected length (4), or use of_property_read_u32.

> +               dev_err(&adapter->dev, "invalid reg on %pOF\n", node);
> +               return ERR_PTR(-EINVAL);
> +       }
> +
> +       info.addr = be32_to_cpup(addr_be);
> +       info.of_node = of_node_get(node);
> +
> +       result = peci_new_device(adapter, &info);
> +       if (!result)

Should you do an of_node_put here?

> +               result = ERR_PTR(-EINVAL);
> +
> +       of_node_put(node);

Why do you release the reference here?

> +       return result;
> +}
> +