linux-kernel - Re: [PATCH v3 2/8] android_pipe: don't be clever with #define offsets

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Date:	Wed, 02 Dec 2015 12:11:09 -0800
From:	Joe Perches <joe@...ches.com>
To:	Jin Qian <jinqian@...roid.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Greg Hackmann <ghackmann@...gle.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Peter Senna Tschudin <peter.senna@...il.com>,
	Jason Hu <jia-cheng.hu@...el.com>,
	Alex Bennée <alex.bennee@...aro.org>,
	Yu Ning <yu.ning@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/8] android_pipe: don't be clever with #define
 offsets

On Wed, 2015-12-02 at 11:35 -0800, Jin Qian wrote:
> From: Alex Bennée <alex.bennee@...aro.org>
> 
> You just make it harder to figure out when commands are being used.
> 
> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
> Signed-off-by: Jin Qian <jinqian@...roid.com>
> ---
>  drivers/platform/goldfish/goldfish_pipe.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
> index e7a29e2..0fb3a34 100644
> --- a/drivers/platform/goldfish/goldfish_pipe.c
> +++ b/drivers/platform/goldfish/goldfish_pipe.c
> @@ -90,12 +90,6 @@
>  #define CMD_WRITE_BUFFER	4  /* send a user buffer to the emulator */
>  #define CMD_WAKE_ON_WRITE	5  /* tell the emulator to wake us when writing
>  				     is possible */
> -
> -/* The following commands are related to read operations, they must be
> - * listed in the same order than the corresponding write ones, since we
> - * will use (CMD_READ_BUFFER - CMD_WRITE_BUFFER) as a special offset
> - * in goldfish_pipe_read_write() below.
> - */
>  #define CMD_READ_BUFFER        6  /* receive a user buffer from the emulator */
>  #define CMD_WAKE_ON_READ       7  /* tell the emulator to wake us when reading
>  				   * is possible */
> @@ -272,8 +266,6 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
>  	unsigned long irq_flags;
>  	struct goldfish_pipe *pipe = filp->private_data;
>  	struct goldfish_pipe_dev *dev = pipe->dev;
> -	const int cmd_offset = is_write ? 0
> -					: (CMD_READ_BUFFER - CMD_WRITE_BUFFER);

This one could be
	int cmd_type = is_write ? CMD_WRITE_BUFFER : CMD_READ_BUFFER;
@@ -325,7 +317,8 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
>  
>  		/* Now, try to transfer the bytes in the current page */
>  		spin_lock_irqsave(&dev->lock, irq_flags);
> -		if (access_with_param(dev, CMD_WRITE_BUFFER + cmd_offset,
> +		if (access_with_param(dev,
> +				is_write ? CMD_WRITE_BUFFER : CMD_READ_BUFFER,
>  				address, avail, pipe, &status)) {
>  			gf_write_ptr(pipe, dev->base + PIPE_REG_CHANNEL,
>  				     dev->base + PIPE_REG_CHANNEL_HIGH);
> @@ -333,7 +326,7 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
>  			gf_write_ptr((void *)address,
>  				     dev->base + PIPE_REG_ADDRESS,
>  				     dev->base + PIPE_REG_ADDRESS_HIGH);
> -			writel(CMD_WRITE_BUFFER + cmd_offset,
> +			writel(is_write ? CMD_WRITE_BUFFER : CMD_READ_BUFFER,
>  					dev->base + PIPE_REG_COMMAND);
>  			status = readl(dev->base + PIPE_REG_STATUS);
>  		}

and the loop could use cmd_type instead of the ?:

> @@ -370,7 +363,8 @@ static ssize_t goldfish_pipe_read_write(struct file *filp, char __user *buffer,
>  		set_bit(wakeBit, &pipe->flags);
>  
>  		/* Tell the emulator we're going to wait for a wake event */
> -		goldfish_cmd(pipe, CMD_WAKE_ON_WRITE + cmd_offset);
> +		goldfish_cmd(pipe,
> +			is_write ? CMD_WAKE_ON_WRITE : CMD_WAKE_ON_READ);
>  
>  		/* Unlock the pipe, then wait for the wake signal */
>  		mutex_unlock(&pipe->lock);

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