linux-kernel - Re: [RFC PATCH v2 1/2] scsi: ufs: Add Multi-Circular Queue support

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Date:   Thu, 18 Aug 2022 13:24:17 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Manivannan Sadhasivam <mani@...nel.org>,
        Can Guo <quic_cang@...cinc.com>
Cc:     quic_asutoshd@...cinc.com, quic_nguyenb@...cinc.com,
        quic_xiaosenh@...cinc.com, stanley.chu@...iatek.com,
        adrian.hunter@...el.com, beanhuo@...ron.com, avri.altman@....com,
        linux-scsi@...r.kernel.org, kernel-team@...roid.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        jongmin jeong <jjmin.jeong@...sung.com>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 1/2] scsi: ufs: Add Multi-Circular Queue support

On 8/12/22 02:10, Manivannan Sadhasivam wrote:
> On Thu, Aug 11, 2022 at 03:33:03AM -0700, Can Guo wrote:
>> +static unsigned int dev_cmd_queue = 1;
>> +static unsigned int read_queues;
> 
> Where is this initialized?

The Linux kernel coding style does not allow to explicitly initialize 
static variables to zero.

>> +
>> +static int rw_queue_count_set(const char *val, const struct kernel_param *kp)
>> +{
>> +	unsigned int n;
>> +	int ret;
>> +
>> +	ret = kstrtouint(val, 10, &n);
>> +	if (ret)
>> +		return ret;
>> +	if (n > num_possible_cpus())
>> +		return -EINVAL;
>> +	return param_set_uint(val, kp);
>> +}
>> +
>> +static const struct kernel_param_ops rw_queue_count_ops = {
>> +	.set = rw_queue_count_set,
>> +	.get = param_get_uint,
>> +};
>> +
>> +static unsigned int rw_queues = 8;
>> +module_param_cb(rw_queues, &rw_queue_count_ops, &rw_queues, 0644);
>> +MODULE_PARM_DESC(rw_queues, "Number of queues used for rw. Default value is 8");
>> +
> 
> Using module params is not encouraged these days. So please switch to Kconfig.

Hmm ... I think using CONFIG_* variables is worse than using module 
parameters since modifying CONFIG_* variables requires rebuilding the 
kernel.

>> +struct cq_entry {
>> +	/* DW 0-1 */
>> +	__le32 command_desc_base_addr_lo;
>> +	__le32 command_desc_base_addr_hi;
>> +
>> +	/* DW 2 */
>> +	__le16  response_upiu_length;
>> +	__le16  response_upiu_offset;
>> +
>> +	/* DW 3 */
>> +	__le16  prd_table_length;
>> +	__le16  prd_table_offset;
>> +
>> +	/* DW 4 */
>> +	__le32 status;
>> +
>> +	/* DW 5-7 */
>> +	u32 reserved[3];
>> +};
> 
> packed?

Using __packed if it is not necessary is wrong since it makes code slower.

Thanks,

Bart.