linux-kernel - Re: [PATCH] nvme-pci: ignore bogus CRTO according to NVME 2.0 spec

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Message-ID: <ca5729af-70db-4126-8973-f9036f41ede9@archlinux.org>
Date:   Tue, 12 Sep 2023 22:07:21 +0300
From:   Felix Yan <felixonmars@...hlinux.org>
To:     Keith Busch <kbusch@...nel.org>
Cc:     highenthalpyh@...il.com, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org, xuwd1@...mail.com, hch@....de
Subject: Re: [PATCH] nvme-pci: ignore bogus CRTO according to NVME 2.0 spec

On 9/12/23 18:44, Keith Busch wrote:
> On Tue, Sep 12, 2023 at 09:26:19AM +0300, Felix Yan wrote:
>>
>> Should we also apply the same max() on the NVME_CRTO_CRIMT branch though?
>> The spec actually says the same thing (Timeout should be FFh) for that too.
> 
> The spec is weird here: the CAP.TO value depends on the CC setting, but
> we read and cache CAP.TO before setting CC, so TO is always associated
> to CRWMT. We'll need to refresh the CAP value after the initial CC
> write, but before final CC.EN.
> 
> ---
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 37b6fa7466620..4adc0b2f12f1e 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -2245,25 +2245,8 @@ int nvme_enable_ctrl(struct nvme_ctrl *ctrl)
>   	else
>   		ctrl->ctrl_config = NVME_CC_CSS_NVM;
>   
> -	if (ctrl->cap & NVME_CAP_CRMS_CRWMS) {
> -		u32 crto;
> -
> -		ret = ctrl->ops->reg_read32(ctrl, NVME_REG_CRTO, &crto);
> -		if (ret) {
> -			dev_err(ctrl->device, "Reading CRTO failed (%d)\n",
> -				ret);
> -			return ret;
> -		}
> -
> -		if (ctrl->cap & NVME_CAP_CRMS_CRIMS) {
> -			ctrl->ctrl_config |= NVME_CC_CRIME;
> -			timeout = NVME_CRTO_CRIMT(crto);
> -		} else {
> -			timeout = NVME_CRTO_CRWMT(crto);
> -		}
> -	} else {
> -		timeout = NVME_CAP_TIMEOUT(ctrl->cap);
> -	}
> +	if (ctrl->cap & NVME_CAP_CRMS_CRWMS && ctrl->cap & NVME_CAP_CRMS_CRIMS)
> +		ctrl->ctrl_config |= NVME_CC_CRIME;
>   
>   	ctrl->ctrl_config |= (NVME_CTRL_PAGE_SHIFT - 12) << NVME_CC_MPS_SHIFT;
>   	ctrl->ctrl_config |= NVME_CC_AMS_RR | NVME_CC_SHN_NONE;
> @@ -2277,6 +2260,33 @@ int nvme_enable_ctrl(struct nvme_ctrl *ctrl)
>   	if (ret)
>   		return ret;
>   
> +	/* CAP value may change after initial CC write */
> +	ret = ctrl->ops->reg_read64(ctrl, NVME_REG_CAP, &ctrl->cap);
> +	if (ret)
> +		return ret;
> +
> +	timeout = NVME_CAP_TIMEOUT(ctrl->cap);
> +	if (ctrl->cap & NVME_CAP_CRMS_CRWMS) {
> +		u32 crto;
> +
> +		ret = ctrl->ops->reg_read32(ctrl, NVME_REG_CRTO, &crto);
> +		if (ret) {
> +			dev_err(ctrl->device, "Reading CRTO failed (%d)\n",
> +				ret);
> +			return ret;
> +		}
> +
> +		/*
> +		 * CRTO should always be greater or equal to CAP.TO, but some
> +		 * devices are known to get this wrong. Use the larger of the
> +		 * two values.
> +		 */
> +		if (ctrl->ctrl_config & NVME_CC_CRIME)
> +			timeout = max(timeout, NVME_CRTO_CRIMT(crto));
> +		else
> +			timeout = max(timeout, NVME_CRTO_CRWMT(crto));
> +	}
> +
>   	ctrl->ctrl_config |= NVME_CC_ENABLE;
>   	ret = ctrl->ops->reg_write32(ctrl, NVME_REG_CC, ctrl->ctrl_config);
>   	if (ret)

Thanks for getting into the details. This looks great to me.

I have also tried it on top of 6.5.2 kernel and verified that it works 
as expected.

-- 
Regards,
Felix Yan


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