linux-kernel - Re: [PATCH 11/14] fsi: Improve master indexing

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Message-ID: <CACPK8Xe1OmLtLrONZmqib6BhDyPHzj+HcOd15MXyK0QVHPTOEg@mail.gmail.com>
Date:   Wed, 9 Aug 2023 07:08:05 +0000
From:   Joel Stanley <joel@....id.au>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     linux-fsi@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        jk@...abs.org, alistair@...ple.id.au, andrew@...id.au,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 11/14] fsi: Improve master indexing

On Mon, 12 Jun 2023 at 19:57, Eddie James <eajames@...ux.ibm.com> wrote:
>
> Master indexing is problematic if a hub is rescanned while the
> root master is being rescanned. Move the IDA free below the device
> unregistration, lock the scan mutex in the probe function, and
> request a specific idx in the hub driver.

I've applied this series, but taking a closer look at this patch I
think it can be improved. If you resend, just send this patch.

>
> Signed-off-by: Eddie James <eajames@...ux.ibm.com>
> ---
>  drivers/fsi/fsi-core.c       | 41 ++++++++++++++++++++++--------------
>  drivers/fsi/fsi-master-hub.c |  2 ++
>  2 files changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
> index ec4d02264391..503061a6740b 100644
> --- a/drivers/fsi/fsi-core.c
> +++ b/drivers/fsi/fsi-core.c
> @@ -1327,46 +1327,55 @@ static struct class fsi_master_class = {
>  int fsi_master_register(struct fsi_master *master)
>  {
>         int rc;
> -       struct device_node *np;
>
>         mutex_init(&master->scan_lock);
> -       master->idx = ida_alloc(&master_ida, GFP_KERNEL);
> +
> +       if (master->idx) {

Why do we allocate a new idx if there's already one?

> +               master->idx = ida_alloc_range(&master_ida, master->idx,
> +                                             master->idx, GFP_KERNEL);

If we can't get one in the range we want, we ask for any? Should this
print a warning?

> +               if (master->idx < 0)
> +                       master->idx = ida_alloc(&master_ida, GFP_KERNEL);
> +       } else {

If ixd was zero, we create one. This is the "normal" case?

> +               master->idx = ida_alloc(&master_ida, GFP_KERNEL);
> +       }
> +

We check the same error condition again.

>         if (master->idx < 0)
>                 return master->idx;

>
> -       dev_set_name(&master->dev, "fsi%d", master->idx);
> +       if (!dev_name(&master->dev))
> +               dev_set_name(&master->dev, "fsi%d", master->idx);
> +
>         master->dev.class = &fsi_master_class;
>
> +       mutex_lock(&master->scan_lock);
>         rc = device_register(&master->dev);
>         if (rc) {
>                 ida_free(&master_ida, master->idx);
> -               return rc;
> -       }
> +       } else {
> +               struct device_node *np = dev_of_node(&master->dev);

This change looks a bit different to the idx changes. What's happening here?
>
> -       np = dev_of_node(&master->dev);
> -       if (!of_property_read_bool(np, "no-scan-on-init")) {
> -               mutex_lock(&master->scan_lock);
> -               fsi_master_scan(master);
> -               mutex_unlock(&master->scan_lock);
> +               if (!of_property_read_bool(np, "no-scan-on-init"))
> +                       fsi_master_scan(master);
>         }
>
> -       return 0;
> +       mutex_unlock(&master->scan_lock);
> +       return rc;
>  }
>  EXPORT_SYMBOL_GPL(fsi_master_register);
>
>  void fsi_master_unregister(struct fsi_master *master)
>  {
> -       trace_fsi_master_unregister(master);
> +       int idx = master->idx;
>
> -       if (master->idx >= 0) {
> -               ida_free(&master_ida, master->idx);
> -               master->idx = -1;
> -       }
> +       trace_fsi_master_unregister(master);
>
>         mutex_lock(&master->scan_lock);
>         fsi_master_unscan(master);
> +       master->n_links = 0;
>         mutex_unlock(&master->scan_lock);
> +
>         device_unregister(&master->dev);
> +       ida_free(&master_ida, idx);
>  }
>  EXPORT_SYMBOL_GPL(fsi_master_unregister);
>
> diff --git a/drivers/fsi/fsi-master-hub.c b/drivers/fsi/fsi-master-hub.c
> index 6d8b6e8854e5..36da643b3201 100644
> --- a/drivers/fsi/fsi-master-hub.c
> +++ b/drivers/fsi/fsi-master-hub.c
> @@ -12,6 +12,7 @@
>  #include <linux/slab.h>
>
>  #include "fsi-master.h"
> +#include "fsi-slave.h"
>
>  #define FSI_ENGID_HUB_MASTER           0x1c
>
> @@ -229,6 +230,7 @@ static int hub_master_probe(struct device *dev)
>         hub->master.dev.release = hub_master_release;
>         hub->master.dev.of_node = of_node_get(dev_of_node(dev));
>
> +       hub->master.idx = fsi_dev->slave->link + 1;
>         hub->master.n_links = links;
>         hub->master.read = hub_master_read;
>         hub->master.write = hub_master_write;
> --
> 2.31.1
>