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References: <20190114130710.427600-1-tmaimon77@gmail.com>
 <20190114130710.427600-4-tmaimon77@gmail.com>
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From: Joel Stanley <joel@jms.id.au>
Date: Wed, 16 Jan 2019 10:53:11 +1100
Message-ID: <CACPK8XeF8MYsUJA7HsQL23mfoGFRQ5rjSTRzrJxhZL23fzRikg@mail.gmail.com>
Subject: Re: [linux dev-4.19 03/15] mtd: spi-nor: add NPCM FIU controller
 driver
To: Tomer Maimon <tmaimon77@gmail.com>
Cc: OpenBMC Maillist <openbmc@lists.ozlabs.org>,
 Andrew Jeffery <andrew@aj.id.au>
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X-List-Received-Date: Tue, 15 Jan 2019 23:53:25 -0000

Hi Tomer,

On Tue, 15 Jan 2019 at 00:07, Tomer Maimon <tmaimon77@gmail.com> wrote:
>
> Add Nuvoton NPCM BMC Flash Interface Unit(FIU) SPI-NOR
> controller driver
>
> The FIU supports single, dual or quad communication interface.
>
> the FIU controller can operate in following modes:
> - User Mode Access(UMA): provides flash access by using an
>   indirect address/data mechanism.
> - direct rd/wr mode: maps the flash memory into the core
>   address space.
> - SPI-X mode: used for an expansion bus to an ASIC or CPLD.
>

> +static int npcm_fiu_uma_read(struct spi_nor *nor, u8 transaction_code,
> +                            u32 address, bool is_address_size, u8 *data,
> +                            u32 data_size)
> +{

> +
> +       regmap_update_bits(host->regmap, NPCM_FIU_UMA_CTS,
> +                          NPCM_FIU_UMA_CTS_DEV_NUM,
> +                          (chip->chipselect <<
> +                           NPCM_FIU_UMA_CTS_DEV_NUM_SHIFT));
> +       regmap_update_bits(host->regmap, NPCM_FIU_UMA_CMD,
> +                          NPCM_FIU_UMA_CMD_CMD, transaction_code);
> +       regmap_write(host->regmap, NPCM_FIU_UMA_ADDR, address);

I notice this driver uses regmap for register reads and writes. Are
you aware that regmap has a very large overhead for every operation?
It takes a few hundred instructions to do each read/write, where as
readl/writel result in one or two instructions.

I'd strongly recommend implementing your drivers without regmap unless
you are using it to access, for example, a couple of registers that
are shared between drivers.

Cheers,

Joel