linux-kernel - Re: [PATCH v4 05/16] ufs: core: mcq: Add Multi Circular Queue support

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Date:   Wed, 9 Nov 2022 13:16:16 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Asutosh Das <quic_asutoshd@...cinc.com>, quic_cang@...cinc.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org
Cc:     quic_nguyenb@...cinc.com, quic_xiaosenh@...cinc.com,
        stanley.chu@...iatek.com, eddie.huang@...iatek.com,
        daejun7.park@...sung.com, avri.altman@....com, mani@...nel.org,
        beanhuo@...ron.com, linux-arm-msm@...r.kernel.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arthur Simchaev <Arthur.Simchaev@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/16] ufs: core: mcq: Add Multi Circular Queue support

On 11/9/22 11:41, Asutosh Das wrote:
> +static int ufshcd_mcq_config_nr_queues(struct ufs_hba *hba)
> +{
> +	int i;
> +	u32 hba_maxq, rem, tot_queues;
> +	struct Scsi_Host *host = hba->host;
> +
> +	hba_maxq = FIELD_GET(GENMASK(7, 0), hba->mcq_capabilities);
> +
> +	if (!rw_queues)
> +		rw_queues = num_possible_cpus();
> +
> +	tot_queues = UFS_MCQ_NUM_DEV_CMD_QUEUES + read_queues + poll_queues +
> +			rw_queues;
> +
> +	if (hba_maxq < tot_queues) {
> +		dev_err(hba->dev, "Total queues (%d) exceeds HC capacity (%d)\n",
> +			tot_queues, hba_maxq);
> +		return -EOPNOTSUPP;
> +	}

This function can fail with default kernel module parameters, e.g. 
num_possible_cpus() == 8 and hba_maxq == 4. This is not acceptable. A 
better solution is required, e.g. reducing rw_queues if the user has not 
set this kernel module parameter.

Thanks,

Bart.