Hi Rob, Mark, Ping, can you please provide your feedback? Even if you have no comments, please say so. Thanks again! On Mon, Jan 7, 2019 at 6:51 PM Geert Uytterhoeven <geert+renesas@xxxxxxxxx> wrote: > Best Wishes for 2019! > > Can you please provide your opinion on parsing the whole device tree for > "resets" phandle properties to find shared resets, cfr. patch [1] below? > > This is a prerequisite for safe generic reset handling for > virtualization on DT-based platforms, cfr. patch [2]. > > Many thanks in advance! > > References: > 1. [PATCH v3] reset: Exclusive resets must be dedicated to a single > hardware block > https://lore.kernel.org/lkml/20181113133520.20889-1-geert+renesas@xxxxxxxxx/ > 2. [PATCH v5] vfio: platform: Add generic reset controller support > https://lore.kernel.org/lkml/20181113131508.18246-1-geert+renesas@xxxxxxxxx/ > > From 96418942472531d736dffd64ff5ae90d055d71b0 Mon Sep 17 00:00:00 2001 > From: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > Date: Mon, 17 Sep 2018 16:34:26 +0200 > Subject: [PATCH v3] reset: Exclusive resets must be dedicated to a single > hardware block > > In some SoCs multiple hardware blocks may share a reset control. > The reset control API for shared resets will only assert such a reset > when the drivers for all hardware blocks agree. > The exclusive reset control API still allows to assert such a reset, but > that impacts all other hardware blocks sharing the reset. > > While the kernel doc comments clearly state that the API for shared > resets applies to reset controls which are shared between hardware > blocks, the exact meaning of exclusive resets is not documented. > Fix the semantic ambiguity with respect to exclusive access vs. > exclusive reset lines by: > 1. Clarifying that exclusive resets really are intended for use with > reset controls which are dedicated to a single hardware block, > 2. Ensuring that obtaining an exclusive reset control will fail if the > reset is shared by multiple hardware blocks, for both DT-based and > lookup-based reset controls. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > --- > Question from Philipp for the DT maintainers: > > "I'd still like to hear the device tree maintainers' opinion on > parsing the whole DT for "resets" phandle properties to find shared > resets like this." > > Thanks! > > v3: > - Make args parameter of __of_reset_is_exclusive() a pointer, > - Print a warning when detecting a shared reset, > - Rebase on top of of_node_put() move, > > v2: > - Fix wrong variable in __reset_is_dedicated() loop, > - Add missing of_node_put() in __of_reset_is_dedicated(), > - Document that exclusive reset controls imply they are dedicated to a > single hardware block, > - Drop new dedicated flag and new API reset_control_get_dedicated(), > as exclusive already implies dedicated, > - Rename {__of_,}reset_is_dedicated() to {__of_,}reset_is_exclusive(), > - Reword description. > > Note: Exclusive lookup-based reset controls were not tested. > --- > drivers/reset/core.c | 67 +++++++++++++++++++++++++++++++++++++++++++ > include/linux/reset.h | 5 +++- > 2 files changed, 71 insertions(+), 1 deletion(-) > > diff --git a/drivers/reset/core.c b/drivers/reset/core.c > index bce2d6aefef98131..022740cfab9f429e 100644 > --- a/drivers/reset/core.c > +++ b/drivers/reset/core.c > @@ -459,6 +459,42 @@ static void __reset_control_put_internal(struct reset_control *rstc) > kref_put(&rstc->refcnt, __reset_control_release); > } > > +static bool __of_reset_is_exclusive(const struct device_node *node, > + const struct of_phandle_args *args, > + const char *id) > +{ > + struct of_phandle_args args2; > + struct device_node *node2; > + int index, ret; > + bool eq; > + > + for_each_node_with_property(node2, "resets") { > + if (node == node2) > + continue; > + > + for (index = 0; ; index++) { > + ret = of_parse_phandle_with_args(node2, "resets", > + "#reset-cells", index, > + &args2); > + if (ret) > + break; > + > + eq = (args2.np == args.np && > + args2.args_count == args.args_count && > + !memcmp(args2.args, args.args, > + args.args_count * sizeof(args.args[0]))); > + of_node_put(args2.np); > + if (eq) { > + pr_warn("%pOF requests exclusive control over reset %s shared with %pOF on %pOF\n", > + node, id, node2, args->np); > + return false; > + } > + } > + } > + > + return true; > +} > + > struct reset_control *__of_reset_control_get(struct device_node *node, > const char *id, int index, bool shared, > bool optional) > @@ -513,6 +549,11 @@ struct reset_control *__of_reset_control_get(struct device_node *node, > goto out; > } > > + if (!shared && !__of_reset_is_exclusive(node, &args, id)) { > + rstc = ERR_PTR(-EINVAL); > + goto out; > + } > + > /* reset_list_mutex also protects the rcdev's reset_control list */ > rstc = __reset_control_get_internal(rcdev, rstc_id, shared); > > @@ -542,6 +583,27 @@ __reset_controller_by_name(const char *name) > return NULL; > } > > +static bool __reset_is_exclusive(const struct reset_control_lookup *lookup) > +{ > + const struct reset_control_lookup *lookup2; > + > + list_for_each_entry(lookup2, &reset_lookup_list, list) { > + if (lookup2 == lookup) > + continue; > + > + if (lookup2->provider == lookup->provider && > + lookup2->index == lookup->index) { > + pr_warn("%s/%s requests exclusive control over reset %s:%u shared with %s/%s", > + lookup->dev_id, lookup->con_id, > + lookup->provider, lookup->index, > + lookup2->dev_id, lookup2->con_id); > + return false; > + } > + } > + > + return true; > +} > + > static struct reset_control * > __reset_control_get_from_lookup(struct device *dev, const char *con_id, > bool shared, bool optional) > @@ -563,6 +625,11 @@ __reset_control_get_from_lookup(struct device *dev, const char *con_id, > if ((!con_id && !lookup->con_id) || > ((con_id && lookup->con_id) && > !strcmp(con_id, lookup->con_id))) { > + if (!shared && !__reset_is_exclusive(lookup)) { > + mutex_unlock(&reset_lookup_mutex); > + return ERR_PTR(-EINVAL); > + } > + > mutex_lock(&reset_list_mutex); > rcdev = __reset_controller_by_name(lookup->provider); > if (!rcdev) { > diff --git a/include/linux/reset.h b/include/linux/reset.h > index b7f3ad691ee9773e..2698b36bd1eb3e0c 100644 > --- a/include/linux/reset.h > +++ b/include/linux/reset.h > @@ -123,8 +123,11 @@ static inline int device_reset_optional(struct device *dev) > * @id: reset line name > * > * Returns a struct reset_control or IS_ERR() condition containing errno. > - * If this function is called more than once for the same reset_control it will > + * If this function is called more than once for the same reset control it will > * return -EBUSY. > + * This function is intended for use with reset controls which are dedicated > + * to a single hardware block. If called for a reset control shared among > + * multiple hardware blocks, it will return -EINVAL. > * > * See reset_control_get_shared for details on shared references to > * reset-controls. > -- > 2.17.1 Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
