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Subject: Re: [PATCHv2] usb: typec: tps6598x: handle block writes separately
 with plain-I2C adapters
To:     Nikolaus Voss <nv@vosn.de>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        nikolaus.voss@loewensteinmedical.de
References: <20180425142209.30745-1-heikki.krogerus@linux.intel.com>
 <20190220110017.BFA344CE86@mail.steuer-voss.de>
 <20190220125731.02E274CFE0@mail.steuer-voss.de>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <be1f988c-5b2f-91cf-d210-1e28c09f106f@roeck-us.net>
Date:   Wed, 20 Feb 2019 06:45:17 -0800
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On 2/20/19 4:57 AM, Nikolaus Voss wrote:
> Commit 1a2f474d328f handles block _reads_ separately with plain-I2C
> adapters, but the problem described with regmap-i2c not handling
> SMBus block transfers (i.e. read and writes) correctly also exists
> with writes.
> 
> As workaround, this patch adds a block write function the same way
> 1a2f474d328f adds a block read function.
> 
> Fixes: 1a2f474d328f ("usb: typec: tps6598x: handle block reads separately with plain-I2C adapters")
> Fixes: 0a4c005bd171 ("usb: typec: driver for TI TPS6598x USB Power Delivery controllers")
> Signed-off-by: Nikolaus Voss <nikolaus.voss@loewensteinmedical.de>
> ---
> v2: fix tps6598x_exec_cmd also
> ---
>   drivers/usb/typec/tps6598x.c | 26 ++++++++++++++++++++------
>   1 file changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/typec/tps6598x.c b/drivers/usb/typec/tps6598x.c
> index c84c8c189e90..c54b73fb2a2f 100644
> --- a/drivers/usb/typec/tps6598x.c
> +++ b/drivers/usb/typec/tps6598x.c
> @@ -110,6 +110,20 @@ tps6598x_block_read(struct tps6598x *tps, u8 reg, void *val, size_t len)
>   	return 0;
>   }
>   
> +static int tps6598x_block_write(struct tps6598x *tps, u8 reg,
> +				void *val, size_t len)
> +{
> +	u8 data[len + 1];
> +

You should use TPS_MAX_LEN + 1 here to avoid the variable length array.
See upstream commit 0bb95f80a38f8 ("Makefile: Globally enable VLA warning")
and 8d361fa2c29dc ("usb: typec: tps6598x: Remove VLA usage"). Not sure if
the WARN_ON introduced by 8d361fa2c29dc is really needed; I dislike
unnecessary runtime checks.

Guenter

> +	if (!tps->i2c_protocol)
> +		return regmap_raw_write(tps->regmap, reg, val, len);
> +
> +	data[0] = len;
> +	memcpy(&data[1], val, len);
> +
> +	return regmap_raw_write(tps->regmap, reg, data, sizeof(data));
> +}
> +
>   static inline int tps6598x_read16(struct tps6598x *tps, u8 reg, u16 *val)
>   {
>   	return tps6598x_block_read(tps, reg, val, sizeof(u16));
> @@ -127,23 +141,23 @@ static inline int tps6598x_read64(struct tps6598x *tps, u8 reg, u64 *val)
>   
>   static inline int tps6598x_write16(struct tps6598x *tps, u8 reg, u16 val)
>   {
> -	return regmap_raw_write(tps->regmap, reg, &val, sizeof(u16));
> +	return tps6598x_block_write(tps, reg, &val, sizeof(u16));
>   }
>   
>   static inline int tps6598x_write32(struct tps6598x *tps, u8 reg, u32 val)
>   {
> -	return regmap_raw_write(tps->regmap, reg, &val, sizeof(u32));
> +	return tps6598x_block_write(tps, reg, &val, sizeof(u32));
>   }
>   
>   static inline int tps6598x_write64(struct tps6598x *tps, u8 reg, u64 val)
>   {
> -	return regmap_raw_write(tps->regmap, reg, &val, sizeof(u64));
> +	return tps6598x_block_write(tps, reg, &val, sizeof(u64));
>   }
>   
>   static inline int
>   tps6598x_write_4cc(struct tps6598x *tps, u8 reg, const char *val)
>   {
> -	return regmap_raw_write(tps->regmap, reg, &val, sizeof(u32));
> +	return tps6598x_block_write(tps, reg, &val, sizeof(u32));
>   }
>   
>   static int tps6598x_read_partner_identity(struct tps6598x *tps)
> @@ -229,8 +243,8 @@ static int tps6598x_exec_cmd(struct tps6598x *tps, const char *cmd,
>   		return -EBUSY;
>   
>   	if (in_len) {
> -		ret = regmap_raw_write(tps->regmap, TPS_REG_DATA1,
> -				       in_data, in_len);
> +		ret = tps6598x_block_write(tps, TPS_REG_DATA1,
> +					   in_data, in_len);
>   		if (ret)
>   			return ret;
>   	}
>