linux-kernel - Re: [PATCH 02/10] regmap: spi: Check raw_[read|write] against max message size

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Message-ID: <20210908130929.GP9223@ediswmail.ad.cirrus.com>
Date:   Wed, 8 Sep 2021 13:09:29 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Lucas Tanure <tanureal@...nsource.cirrus.com>
CC:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Sanjay R Mehta <sanju.mehta@....com>,
        Nehal Bakulchandra Shah <Nehal-Bakulchandra.shah@....com>,
        <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH 02/10] regmap: spi: Check raw_[read|write] against max
 message size

On Wed, Sep 08, 2021 at 12:34:43PM +0100, Lucas Tanure wrote:
> regmap-spi will split data and address between two transfers
> in the same message, so max_[read|write] must include space
> for the address and padding
> 
> Signed-off-by: Lucas Tanure <tanureal@...nsource.cirrus.com>
> ---
>  drivers/base/regmap/regmap-spi.c |  4 ++++
>  drivers/base/regmap/regmap.c     | 15 +++++++++++++++
>  include/linux/regmap.h           |  3 +++
>  3 files changed, 22 insertions(+)
> 
> diff --git a/drivers/base/regmap/regmap-spi.c b/drivers/base/regmap/regmap-spi.c
> index 0e6552e57ecf..1434c502e340 100644
> --- a/drivers/base/regmap/regmap-spi.c
> +++ b/drivers/base/regmap/regmap-spi.c
> @@ -123,6 +123,10 @@ static const struct regmap_bus *regmap_get_spi_bus(struct spi_device *spi,
>  		bus->free_on_exit = true;
>  		bus->max_raw_read = max_size;
>  		bus->max_raw_write = max_size;
> +
> +		if (spi_max_message_size(spi) != SIZE_MAX)
> +			bus->max_combined_rw = spi_max_message_size(spi);

I am not sure max_combined_rw is the best name here, it makes
sense in a SPI context where reads are a write followed by a
read. But does it really make sense for all buses? Like an MMIO
this no longer seems a very meaningful name.

Perhaps max_transaction? But I am often not the best at thinking
of names myself.

> +
>  		return bus;
>  	}
>  
> diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
> index fe3e38dd5324..1cd936e097b0 100644
> --- a/drivers/base/regmap/regmap.c
> +++ b/drivers/base/regmap/regmap.c
> @@ -718,6 +718,7 @@ struct regmap *__regmap_init(struct device *dev,
>  	struct regmap *map;
>  	int ret = -EINVAL;
>  	enum regmap_endian reg_endian, val_endian;
> +	size_t reg_pad_size;
>  	int i, j;
>  
>  	if (!config)
> @@ -815,6 +816,20 @@ struct regmap *__regmap_init(struct device *dev,
>  	if (bus) {
>  		map->max_raw_read = bus->max_raw_read;
>  		map->max_raw_write = bus->max_raw_write;
> +		if (bus->max_combined_rw) {
> +			reg_pad_size = map->format.reg_bytes + map->format.pad_bytes;

Maybe reg_overhead_size or something? This line uses pad to both
mean the actual padding in pad_bytes and to mean address +
padding in reg_pad_size.

Thanks,
Charles