Re: [PATCH RESEND v2] mtd: physmap: Add Baikal-T1 physically mapped ROMs support

[Vignesh Raghavendra <vigneshr@xxxxxx>]

Hi,

On 27/05/20 4:28 am, Serge Semin wrote:
> Baikal-T1 Boot Controller provides an access to a RO storages, which are
> physically mapped into the MMIO space. In particularly there are the
> Internal ROM embedded into the SoC with a pre-installed firmware,
> externally attached SPI flash (also accessed in the read-only mode) and a
> memory region, which mirrors one of them in accordance with the currently
> enabled system boot mode (also called Boot ROM).
> 
> This commit adds the ROMs support to the physmap driver of the MTD kernel
> subsystem. Currently the driver only supports the Internal ROM, since
> physically mapped SPI flash is utilized by the Baikal-T1 System Boot
> Controller driver so won't be available over mtd-rom interface and
> the Boot ROM mirror mapping has dependency on the SPI flash mapping
> switcher available within the SPI flash registers space. The real access
> to the Boot ROM memory will be added in future.
> 
> Note we had to create a dedicated code for the ROMs since read from the
> corresponding memory regions must be done via the dword-aligned addresses.
> In addition the driver in future states will have to take into account
> that the Boot ROM might mirror the SPI flash region so before accessing it
> the SPI flash direct mapping must be enabled by means of a dedicated flag
> in the Baikal-T1 System SPI register flag.
> 
> Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Maxim Kaurkin <Maxim.Kaurkin@xxxxxxxxxxxxxxxxxxxx>
> Cc: Pavel Parkhomenko <Pavel.Parkhomenko@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ramil Zaripov <Ramil.Zaripov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ekaterina Skachko <Ekaterina.Skachko@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vadim Vlasov <V.Vlasov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alexey Kolotnikov <Alexey.Kolotnikov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Lee Jones <lee.jones@xxxxxxxxxx>
> Cc: linux-mips@xxxxxxxxxxxxxxx
> 
> ---
> 
> Miquel, Richard, Vignesh, the merge window is upon us, please review/merge
> in/whatever this patch.
> 
> This patchset is rebased and tested on the mainline Linux kernel 5.7-rc4:
> base-commit: 0e698dfa2822 ("Linux 5.7-rc4")
> tag: v5.7-rc4
> 
> New vendor prefix will be added in the framework of the next patchset:
> https://lkml.org/lkml/2020/5/6/1047


Sorry, driver patch and dt bindings have to be proposed together...
Driver cannot be accepted ahead of DT bindings been reviewed.

> 
> Note since the next patchset is no longer relevant (as a result of a
> discussion with @Lee and @Miquel)
> https://lkml.org/lkml/2020/3/6/421
> and Boot ROM mtd is currently unsupported I can freely submit this patch,
> while in former case I had to wait for the patchset merged.
> 

[...]
> +static void __xipram bt1_rom_map_copy_from(struct map_info *map,
> +					   void *to, unsigned long from,
> +					   ssize_t len)
> +{
> +	void __iomem *src = map->virt + from;
> +	ssize_t shift, chunk;
> +	u32 data;
> +
> +	if (len <= 0 || from >= map->size)
> +		return;
> +
> +	/* Make sure we don't go over the map limit. */
> +	len = min_t(ssize_t, map->size - from, len);
> +
> +	/*
> +	 * Since requested data size can be pretty big we have to implement
> +	 * the copy procedure as optimal as possible. That's why it's split
> +	 * up into the next three stages: unaligned head, aligned body,
> +	 * unaligned tail.
> +	 */
> +	shift = (ssize_t)src & 0x3;
> +	if (shift) {
> +		chunk = min_t(ssize_t, 4 - shift, len);
> +		data = readl_relaxed(src - shift);
> +		memcpy(to, &data + shift, chunk);
> +		src += chunk;
> +		to += chunk;
> +		len -= chunk;
> +	}
> +
> +	while (len >= 4) {
> +		data = readl_relaxed(src);
> +		memcpy(to, &data, 4);
> +		src += 4;
> +		to += 4;
> +		len -= 4;
> +	}
> +
> +	if (len) {
> +		data = readl_relaxed(src);
> +		memcpy(to, &data, len);
> +	}
> +}
> +
> +static map_word __xipram bt1_rom_dummy_read(struct map_info *map,
> +					  unsigned long ofs)
> +{
> +	map_word ret;
> +
> +	ret.x[0] = 0xFF;
> +
> +	return ret;
> +}

Why define dummy_io for "baikal,bt1-boot-rom"? I don't see any use of
adding a driver that always reads 0xFFs


> +
> +/*
> + * Currently Baikal-T1 SoC internal ROM is only supported. Boot ROM region is
> + * dummy-data filled for now since in case of the system booted up from an
> + * external SPI flash the ROM will mirror the Baikal-T1 System Boot SPI direct
> + * mapping memory region. That region can be only accessed when transparent
> + * mode is enabled, which we unable to do here because this feature is provided
> + * by the SPI controller config space occupied by the corresponding driver.
> + * In future we'll export the mode setting method from the Baikal-T1 System
> + * Boot SPI Controller driver to also have the Boot ROM supported here.
> + */
> +static const struct of_device_id bt1_rom_of_match[] = {
> +	{
> +		.compatible = "baikal,bt1-int-rom",
> +		.data = &bt1_rom_normal_io
> +	},

> +	{
> +		.compatible = "baikal,bt1-boot-rom",
> +		.data = &bt1_rom_dummy_io
> +	},
> +	{ }



[...]

Regards
Vignesh

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