From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Junhao He <hejunhao3@huawei.com>, <linuxarm@huawei.com>
Cc: <suzuki.poulose@arm.com>, <james.clark@arm.com>,
<coresight@lists.linaro.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <jonathan.cameron@huawei.com>,
<yangyicong@huawei.com>, <prime.zeng@hisilicon.com>
Subject: Re: [PATCH 2/3] coresight: ultrasoc-smb: simplify the code for check to_copy valid
Date: Thu, 19 Oct 2023 14:35:48 +0100 [thread overview]
Message-ID: <20231019143530.00004c75@huawei.com> (raw)
In-Reply-To: <20231012094706.21565-3-hejunhao3@huawei.com>
On Thu, 12 Oct 2023 17:47:05 +0800
Junhao He <hejunhao3@huawei.com> wrote:
> We only need to check once when before using the to_copy variable
> to simplify the code.
>
> Signed-off-by: Junhao He <hejunhao3@huawei.com>
I'm not convinced this one is an improvement. Sometimes it's easier to just
see the individual conditions checked even if we could combine them.
It's easy to understand we don't copy data if:
a) We ask for 0 data.
b) There is 0 data
Less easy to establish that with the extra wrap around code in there
(even though that has no impact on to_copy if it is 0)
Jonathan
> ---
> drivers/hwtracing/coresight/ultrasoc-smb.c | 13 ++++---------
> 1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
> index b08a619d1116..e78edc3480ce 100644
> --- a/drivers/hwtracing/coresight/ultrasoc-smb.c
> +++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
> @@ -127,20 +127,15 @@ static ssize_t smb_read(struct file *file, char __user *data, size_t len,
> struct smb_drv_data, miscdev);
> struct smb_data_buffer *sdb = &drvdata->sdb;
> struct device *dev = &drvdata->csdev->dev;
> - ssize_t to_copy = 0;
> -
> - if (!len)
> - return 0;
> -
> - if (!sdb->data_size)
> - return 0;
> -
> - to_copy = min(sdb->data_size, len);
> + ssize_t to_copy = min(sdb->data_size, len);
>
> /* Copy parts of trace data when read pointer wrap around SMB buffer */
> if (sdb->buf_rdptr + to_copy > sdb->buf_size)
> to_copy = sdb->buf_size - sdb->buf_rdptr;
>
> + if (!to_copy)
> + return 0;
> +
> if (copy_to_user(data, sdb->buf_base + sdb->buf_rdptr, to_copy)) {
> dev_dbg(dev, "Failed to copy data to user\n");
> return -EFAULT;
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next prev parent reply other threads:[~2023-10-19 13:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-12 9:47 [PATCH 0/3] Fixed some issues and cleanup of ultrasoc-smb Junhao He
2023-10-12 9:47 ` [PATCH 1/3] coresight: ultrasoc-smb: fix sleep while close preempt in enable_smb Junhao He
2023-10-19 3:05 ` Yicong Yang
2023-10-19 12:45 ` hejunhao
2023-10-19 13:30 ` Jonathan Cameron
2023-10-21 7:25 ` hejunhao
2023-10-12 9:47 ` [PATCH 2/3] coresight: ultrasoc-smb: simplify the code for check to_copy valid Junhao He
2023-10-19 13:35 ` Jonathan Cameron [this message]
2023-10-20 2:33 ` hejunhao
2023-10-12 9:47 ` [PATCH 3/3] coresight: ultrasoc-smb: fix uninitialized before use buf_hw_base Junhao He
2023-10-19 2:34 ` Yicong Yang
2023-10-19 13:08 ` hejunhao
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