Quoting Janek Kotas (2018-11-14 07:24:39)
> This patch adds a driver for Fixed MMIO clock.
> The driver reads a clock frequency value from a single 32-bit memory
> mapped register and registers it as a fixed rate clock.
>
> It can be enabled with COMMON_CLK_FIXED_MMIO Kconfig option.
>
> Signed-off-by: Jan Kotas <jank@xxxxxxxxxxx>
Sounds like a fine idea. Except I can see how it will be abused if there
are a handful of these fixed rate "clks" somewhere in memory that all
get populated.
Do you really have a fixed rate clk in hardware that exposes a single
register, or do you have a set of them that some firmware is populating
into an I/O memory space that we can read the fixed rates from? If it's
the latter, I wonder why we can't just have the firmware populate the
fixed rate clks into DT itself?
> diff --git a/drivers/clk/clk-fixed-mmio.c b/drivers/clk/clk-fixed-mmio.c
> new file mode 100644
> index 0000000000..bbcadab345
> --- /dev/null
> +++ b/drivers/clk/clk-fixed-mmio.c
> @@ -0,0 +1,49 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Memory Mapped IO Fixed Clock driver
> + *
> + * Copyright (C) 2018 Cadence Design Systems, Inc.
> + *
> + * Authors:
> + * Jan Kotas <jank@xxxxxxxxxxx>
> + */
> +
> +#include <linux/clk.h>
Is this include used?
> +#include <linux/clk-provider.h>
> +#include <linux/of_address.h>
> +#include <linux/regmap.h>
Is this include used?
> +
> +static void __init of_fixed_mmio_clk_setup(struct device_node *node)
> +{
> + struct clk *clk;
> + const char *clk_name = node->name;
> + void __iomem *base;
> + u32 clk_freq;
> +
> + base = of_iomap(node, 0);
> + if (!base) {
> + pr_err("%pOFn: failed to map address\n", node);
> + return;
> + }
> +
> + clk_freq = readl(base);
> + iounmap(base);
> + of_property_read_string(node, "clock-output-names", &clk_name);
> +
> + clk = clk_register_fixed_rate(NULL, clk_name, NULL, 0, clk_freq);
> + if (IS_ERR(clk)) {
> + pr_err("%pOFn: failed to register fixed rate clock\n", node);
> + return;
> + }
> +
> + if (of_clk_add_provider(node, of_clk_src_simple_get, clk)) {
> + pr_err("%pOFn: failed to add clock provider\n", node);
> + return;
> + }
> +
> + pr_info("%pOFn: registered fixed-mmio-clock at %u Hz\n",
> + node, clk_freq);
Please no "I'm alive!" messages.
> +}
> +
> +CLK_OF_DECLARE(fixed_mmio_clk, "fixed-mmio-clock", of_fixed_mmio_clk_setup);
Any reason why this can't be a platform driver? It would make this much
less DT specific and usable on other firmwares/platforms if we used a
platform driver here.
