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    SubjectRe: [PATCH] pstore/ram: Improve backward compatibility with older Chromebooks
    On Fri, May 3, 2019 at 10:48 AM Douglas Anderson <dianders@chromium.org> wrote:
    >
    > When you try to run an upstream kernel on an old ARM-based Chromebook
    > you'll find that console-ramoops doesn't work.
    >
    > Old ARM-based Chromebooks, before <https://crrev.com/c/439792>
    > ("ramoops: support upstream {console,pmsg,ftrace}-size properties")
    > used to create a "ramoops" node at the top level that looked like:
    >
    > / {
    > ramoops {
    > compatible = "ramoops";
    > reg = <...>;
    > record-size = <...>;
    > dump-oops;
    > };
    > };
    >
    > ...and these Chromebooks assumed that the downstream kernel would make
    > console_size / pmsg_size match the record size. The above ramoops
    > node was added by the firmware so it's not easy to make any changes.
    >
    > Let's match the expected behavior, but only for those using the old
    > backward-compatible way of working where ramoops is right under the
    > root node.
    >
    > NOTE: if there are some out-of-tree devices that had ramoops at the
    > top level, left everything but the record size as 0, and somehow
    > doesn't want this behavior, we can try to add more conditions here.
    >
    > Signed-off-by: Douglas Anderson <dianders@chromium.org>

    Reviewed-by: Guenter Roeck <groeck@chromium.org>

    > ---
    >
    > fs/pstore/ram.c | 18 ++++++++++++++++++
    > 1 file changed, 18 insertions(+)
    >
    > diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
    > index c5c685589e36..8df3bfa2837f 100644
    > --- a/fs/pstore/ram.c
    > +++ b/fs/pstore/ram.c
    > @@ -669,6 +669,7 @@ static int ramoops_parse_dt(struct platform_device *pdev,
    > struct ramoops_platform_data *pdata)
    > {
    > struct device_node *of_node = pdev->dev.of_node;
    > + struct device_node *parent_node;
    > struct resource *res;
    > u32 value;
    > int ret;
    > @@ -703,6 +704,23 @@ static int ramoops_parse_dt(struct platform_device *pdev,
    >
    > #undef parse_size
    >
    > + /*
    > + * Some old Chromebooks relied on the kernel setting the console_size
    > + * and pmsg_size to the record size since that's what the downstream
    > + * kernel did. These same Chromebooks had "ramoops" straight under
    > + * the root node which isn't according to the upstream bindings. Let's
    > + * make those old Chromebooks work by detecting this and mimicing the
    > + * expected behavior.
    > + */
    > + parent_node = of_get_parent(of_node);
    > + if (of_node_is_root(parent_node) &&
    > + !pdata->console_size && !pdata->ftrace_size &&
    > + !pdata->pmsg_size && !pdata->ecc_info.ecc_size) {
    > + pdata->console_size = pdata->record_size;
    > + pdata->pmsg_size = pdata->record_size;
    > + }
    > + of_node_put(parent_node);
    > +
    > return 0;
    > }
    >
    > --
    > 2.21.0.1020.gf2820cf01a-goog
    >

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