Re: [cip-dev] [PATCH 4.19.y-cip 6/7] spi: spi-mem: Add a new API to support direct mapping

From: "Pavel Machek" <pavel@denx.de>
To: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Cc: cip-dev@lists.cip-project.org,
	Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>,
	Pavel Machek <pavel@denx.de>,
	Biju Das <biju.das.jz@bp.renesas.com>
Subject: Re: [cip-dev] [PATCH 4.19.y-cip 6/7] spi: spi-mem: Add a new API to support direct mapping
Date: Mon, 23 Nov 2020 20:46:26 +0100	[thread overview]
Message-ID: <20201123194626.GD5619@amd> (raw)
In-Reply-To: <20201123120354.26413-7-prabhakar.mahadev-lad.rj@bp.renesas.com>

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Hi!

> commit aa167f3fed0c37e0e4c707d4331d827661f46644 upstream.
> 
> Most modern SPI controllers can directly map a SPI memory (or a portion
> of the SPI memory) in the CPU address space. Most of the time this
> brings significant performance improvements as it automates the whole
> process of sending SPI memory operations every time a new region is
> accessed.
> 
> This new API allows SPI memory drivers to create direct mappings and
> then use them to access the memory instead of using
> spi_mem_exec_op().

> + * Return: the amount of data read from the memory device or a negative error
> + * code. Note that the returned size might be smaller than @len, and the caller
> + * is responsible for calling spi_mem_dirmap_read() again when that happens.
> + */
> +ssize_t spi_mem_dirmap_read(struct spi_mem_dirmap_desc *desc,
> +			    u64 offs, size_t len, void *buf)
> +{
> +	struct spi_controller *ctlr = desc->mem->spi->controller;
> +	ssize_t ret;
> +
> +	if (desc->info.op_tmpl.data.dir != SPI_MEM_DATA_IN)
> +		return -EINVAL;
> +
> +	if (!len)
> +		return 0;
> +
> +	if (desc->nodirmap) {
> +		ret = spi_mem_no_dirmap_read(desc, offs, len, buf);

I'd do return ... here.

> +	} else if (ctlr->mem_ops && ctlr->mem_ops->dirmap_read) {
> +		ret = spi_mem_access_start(desc->mem);
> +		if (ret)
> +			return ret;
> +
> +		ret = ctlr->mem_ops->dirmap_read(desc, offs, len, buf);
> +
> +		spi_mem_access_end(desc->mem);

and here.

> +	} else {
> +		ret = -ENOTSUPP;
> +	}

To help with if/else nesting. spi_mem_dirmap_write could use same
treatment.

Best regards,
								Pavel

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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