linux-kernel - Re: [PATCH v2 1/3] drivers/of: recognize status property of dt memory nodes

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Date:   Thu, 15 Sep 2016 08:43:08 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Bharata B Rao <bharata@...ux.vnet.ibm.com>,
        Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Alistair Popple <apopple@....ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/3] drivers/of: recognize status property of dt memory nodes

On Wed, Sep 14, 2016 at 3:06 PM, Reza Arbab <arbab@...ux.vnet.ibm.com> wrote:
> Respect the standard dt "status" property when scanning memory nodes in
> early_init_dt_scan_memory(), so that if the property is present and not
> "okay", no memory will be added.
>
> The use case at hand is accelerator or device memory, which may be
> unusable until post-boot initialization of the memory link. Such a node
> can be described in the dt as any other, given its status is "disabled".
> Per the device tree specification,
>
> "disabled"
>         Indicates that the device is not presently operational, but it
>         might become operational in the future (for example, something
>         is not plugged in, or switched off).
>
> Once such memory is made operational, it can then be hotplugged.
>
> Signed-off-by: Reza Arbab <arbab@...ux.vnet.ibm.com>
> ---
>  drivers/of/fdt.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 085c638..fc19590 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -1022,8 +1022,10 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
>                                      int depth, void *data)
>  {
>         const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
> +       const char *status;
>         const __be32 *reg, *endp;
>         int l;
> +       bool add_memory;
>
>         /* We are scanning "memory" nodes only */
>         if (type == NULL) {
> @@ -1044,6 +1046,9 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
>
>         endp = reg + (l / sizeof(__be32));
>
> +       status = of_get_flat_dt_prop(node, "status", NULL);
> +       add_memory = !status || !strcmp(status, "okay");

Move this into it's own function to mirror the unflattened version
(of_device_is_available). Also, make sure the logic is the same. IIRC,
"ok" is also allowed.

> +
>         pr_debug("memory scan node %s, reg size %d,\n", uname, l);
>
>         while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
> @@ -1057,6 +1062,9 @@ int __init early_init_dt_scan_memory(unsigned long node, const char *uname,
>                 pr_debug(" - %llx ,  %llx\n", (unsigned long long)base,
>                     (unsigned long long)size);
>
> +               if (!add_memory)
> +                       continue;

There's no point in checking this in the loop. status applies to the
whole node. Just return up above.

Rob