linux-kernel - Re: [PATCH 2/2] mfd: Add Baikal-T1 Boot Controller driver

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Date:   Wed, 25 Mar 2020 10:09:40 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Sergey.Semin@...kalelectronics.ru
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mfd: Add Baikal-T1 Boot Controller driver

On Fri, 06 Mar 2020, Sergey.Semin@...kalelectronics.ru wrote:

> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> Baikal-T1 Boot Controller is an IP block embedded into the SoC and
> responsible for the chip proper pre-initialization and further
> booting up from some memory device. From the Linux kernel point of view
> it's just a multi-functional device, which exports three physically mapped
> ROMs and a single SPI controller.
> 
> Primarily the ROMs are intended to be used for transparent access of
> the memory devices with system bootup code. First ROM device is an
> embedded into the SoC firmware, which is supposed to be used just for
> the chip debug and tests. Second ROM device provides a MMIO-based
> access to an external SPI flash. Third ROM mirrors either the Internal
> or SPI ROM region, depending on the state of the external BOOTCFG_{0,1}
> chip pins selecting the system boot device.
> 
> External SPI flash can be also accessed by the DW APB SSI SPI controller
> embedded into the Baikal-T1 Boot Controller. In this case the memory mapped
> SPI flash region shouldn't be accessed.
> 
> Taking into account all the peculiarities described above, we created
> an MFD-based driver for the Baikal-T1 controller. Aside from ordinary
> OF-based sub-device registration it also provides a simple API to
> serialize an access to the external SPI flash from either the MMIO-based
> SPI interface or embedded SPI controller.

Not sure why this is being classified as an MFD.

This is clearly 'just' a memory device.

> Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> Signed-off-by: Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Paul Burton <paulburton@...nel.org>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> ---
>  drivers/mfd/Kconfig              |  13 ++
>  drivers/mfd/Makefile             |   1 +
>  drivers/mfd/bt1-boot-ctl.c       | 345 +++++++++++++++++++++++++++++++
>  include/linux/mfd/bt1-boot-ctl.h |  46 +++++
>  4 files changed, 405 insertions(+)
>  create mode 100644 drivers/mfd/bt1-boot-ctl.c
>  create mode 100644 include/linux/mfd/bt1-boot-ctl.h

[...]

> diff --git a/drivers/mfd/bt1-boot-ctl.c b/drivers/mfd/bt1-boot-ctl.c
> new file mode 100644
> index 000000000000..9e3cd47a2e7a
> --- /dev/null
> +++ b/drivers/mfd/bt1-boot-ctl.c
> @@ -0,0 +1,345 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
> + *
> + * Authors:
> + *   Serge Semin <Sergey.Semin@...kalelectronics.ru>
> + *
> + * Baikal-T1 Boot Controller driver.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/device.h>
> +#include <linux/platform_device.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/clk.h>
> +#include <linux/mutex.h>
> +#include <linux/mfd/core.h>

Despite including the MFD API, I don't see it being used at all.

> +#include <linux/mfd/bt1-boot-ctl.h>

[...]

> +static inline u32 bc_read(void __iomem *reg)
> +{
> +	return readl(reg);
> +}
> +
> +static inline void bc_write(void __iomem *reg, u32 data)
> +{
> +	writel(data, reg);
> +}

Abstraction for the sake of abstraction is generally discouraged.

[...]

> +static int bc_register_devices(struct bt1_bc *bc)
> +{
> +	int ret;
> +
> +	ret = devm_of_platform_populate(bc->dev);
> +	if (ret)
> +		dev_err(bc->dev, "Failed to add sub-devices\n");
> +
> +	return ret;
> +}

You can call devm_of_platform_populate() from anywhere.

Doesn't have to be an MFD.

[...]

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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