linux-kernel - Re: [PATCH v2 1/1] scsi: ufs: make UFS Tx lane1 clock optional for QCOM platforms

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Date:   Thu, 11 Oct 2018 13:21:28 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     cang@...eaurora.org
Cc:     subhashj@...eaurora.org, Asutosh Das <asutoshd@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Evan Green <evgreen@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        jejb@...ux.vnet.ibm.com,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        venkatg@...eaurora.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] scsi: ufs: make UFS Tx lane1 clock optional for
 QCOM platforms

Hi,

On Thu, Oct 11, 2018 at 5:33 AM Can Guo <cang@...eaurora.org> wrote:
>  static int ufs_qcom_host_clk_get(struct device *dev,
> -               const char *name, struct clk **clk_out)
> +               const char *name, struct clk **clk_out, bool optional)
>  {
>         struct clk *clk;
>         int err = 0;
>
>         clk = devm_clk_get(dev, name);
> -       if (IS_ERR(clk)) {
> +       if (clk == ERR_PTR(-EPROBE_DEFER)) {
> +               err = -EPROBE_DEFER;
> +               dev_warn(dev, "required clock %s hasn't probed yet, err %d\n",
> +                               name, err);
> +       } else if (IS_ERR(clk)) {
> +               if (optional)
> +                       return 0;

Change this function to:

static int ufs_qcom_host_clk_get(struct device *dev,
    const char *name, struct clk **clk_out, bool optional)
{
  struct clk *clk;
  int err;

  clk = devm_clk_get(dev, name);
  if (!IS_ERR(clk)) {
    *clk_out = clk;
    return 0;
  }

  err = PTR_ERR(clk);

  if (optional && err == -ENOENT) {
    *clk_out = NULL;
    return 0;
  }

  if (err != -EPROBE_DEFER)
    dev_err(dev, "failed to get %s err %d",
        name, err);

  return err;
}

Specifically:

* Typically it just spams the log to print something when you see an
-EPROBE_DEFER.

* If a clock is optional you should only consider things a success
only if "-ENOENT" was returned.  All other errors should be considered
fatal.

* If a clock is optional it's slightly cleaner to set *clk_out to
NULL.  I know you're initting global data that happened to already be
NULL by default, but it still feels nice for the abstraction of the
function to do this.

* Please don't pass __func__ to your error messages.


>                 err = PTR_ERR(clk);
>                 dev_err(dev, "%s: failed to get %s err %d",
>                                 __func__, name, err);
> @@ -113,10 +119,10 @@ static void ufs_qcom_disable_lane_clks(struct ufs_qcom_host *host)
>         if (!host->is_lane_clks_enabled)
>                 return;
>
> -       if (host->hba->lanes_per_direction > 1)
> +       if (host->tx_l1_sync_clk)

Remove this "if".  Always call clk_disable_unprepare() which will be a
no-op if "host->tx_l1_sync_clk" is NULL.  clk_disable_unprepare() is a
no-op for NULL clocks by design specifically to make code like this
cleaner.


>                 clk_disable_unprepare(host->tx_l1_sync_clk);
>         clk_disable_unprepare(host->tx_l0_sync_clk);
> -       if (host->hba->lanes_per_direction > 1)
> +       if (host->rx_l1_sync_clk)

Remove this "if".  Always call clk_disable_unprepare() which will be a
no-op if "host->rx_l1_sync_clk" is NULL.  clk_disable_unprepare() is a
no-op for NULL clocks by design specifically to make code like this
cleaner.


>                 clk_disable_unprepare(host->rx_l1_sync_clk);
>         clk_disable_unprepare(host->rx_l0_sync_clk);
>
> @@ -141,12 +147,14 @@ static int ufs_qcom_enable_lane_clks(struct ufs_qcom_host *host)
>         if (err)
>                 goto disable_rx_l0;
>
> -       if (host->hba->lanes_per_direction > 1) {
> +       if (host->rx_l1_sync_clk) {

Remove this "if".  Always call ufs_qcom_host_clk_enable().  The
clk_prepare_enable() inside ufs_qcom_host_clk_enable() will be a no-op
if "host->rx_l1_sync_clk" is NULL and will return 0 (no error).


>                 err = ufs_qcom_host_clk_enable(dev, "rx_lane1_sync_clk",
>                         host->rx_l1_sync_clk);
>                 if (err)
>                         goto disable_tx_l0;
> +       }
>
> +       if (host->tx_l1_sync_clk) {

Remove this "if".  Always call ufs_qcom_host_clk_enable().  The
clk_prepare_enable() inside ufs_qcom_host_clk_enable() will be a no-op
if "host->tx_l1_sync_clk" is NULL and will return 0 (no error).


-Doug