linux-kernel - Re: [RFC PATCH v2 03/18] iommu/riscv: Use data structure instead of individual values

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Message-ID:
 <TY1PPFCDFFFA68A794163FFB7BFAAAC22BEF31CA@TY1PPFCDFFFA68A.apcprd02.prod.outlook.com>
Date: Wed, 24 Sep 2025 11:25:59 +0800
From: "Nutty.Liu" <nutty.liu@...mail.com>
To: Andrew Jones <ajones@...tanamicro.com>, iommu@...ts.linux.dev,
 kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: jgg@...dia.com, zong.li@...ive.com, tjeznach@...osinc.com,
 joro@...tes.org, will@...nel.org, robin.murphy@....com, anup@...infault.org,
 atish.patra@...ux.dev, tglx@...utronix.de, alex.williamson@...hat.com,
 paul.walmsley@...ive.com, palmer@...belt.com, alex@...ti.fr
Subject: Re: [RFC PATCH v2 03/18] iommu/riscv: Use data structure instead of
 individual values

On 9/21/2025 4:38 AM, Andrew Jones wrote:
> From: Zong Li <zong.li@...ive.com>
>
> The parameter will be increased when we need to set up more fields
> in the device context. Use a data structure to wrap them up.
>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> Signed-off-by: Andrew Jones <ajones@...tanamicro.com>
> ---
>   drivers/iommu/riscv/iommu.c | 31 +++++++++++++++++++------------
>   1 file changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
> index 901d02529a26..a44c67a848fa 100644
> --- a/drivers/iommu/riscv/iommu.c
> +++ b/drivers/iommu/riscv/iommu.c
> @@ -988,7 +988,7 @@ static void riscv_iommu_iotlb_inval(struct riscv_iommu_domain *domain,
>    * interim translation faults.
>    */
>   static void riscv_iommu_iodir_update(struct riscv_iommu_device *iommu,
> -				     struct device *dev, u64 fsc, u64 ta)
> +				     struct device *dev, struct riscv_iommu_dc *new_dc)
>   {
>   	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
>   	struct riscv_iommu_dc *dc;
> @@ -1022,10 +1022,10 @@ static void riscv_iommu_iodir_update(struct riscv_iommu_device *iommu,
>   	for (i = 0; i < fwspec->num_ids; i++) {
>   		dc = riscv_iommu_get_dc(iommu, fwspec->ids[i]);
>   		tc = READ_ONCE(dc->tc);
> -		tc |= ta & RISCV_IOMMU_DC_TC_V;
> +		tc |= new_dc->ta & RISCV_IOMMU_DC_TC_V;
>   
> -		WRITE_ONCE(dc->fsc, fsc);
> -		WRITE_ONCE(dc->ta, ta & RISCV_IOMMU_PC_TA_PSCID);
> +		WRITE_ONCE(dc->fsc, new_dc->fsc);
> +		WRITE_ONCE(dc->ta, new_dc->ta & RISCV_IOMMU_PC_TA_PSCID);
Seems it will override all other fields in 'TA' except for the field of 
'PSCID'.
Should the other fields remain unchanged ?
Otherwise,
Reviewed-by: Nutty Liu <nutty.liu@...mail.com>

Thanks,
Nutty
>   		/* Update device context, write TC.V as the last step. */
>   		dma_wmb();
>   		WRITE_ONCE(dc->tc, tc);
> @@ -1304,20 +1304,20 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
>   	struct riscv_iommu_domain *domain = iommu_domain_to_riscv(iommu_domain);
>   	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
>   	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
> -	u64 fsc, ta;
> +	struct riscv_iommu_dc dc = {0};
>   
>   	if (!riscv_iommu_pt_supported(iommu, domain->pgd_mode))
>   		return -ENODEV;
>   
> -	fsc = FIELD_PREP(RISCV_IOMMU_PC_FSC_MODE, domain->pgd_mode) |
> -	      FIELD_PREP(RISCV_IOMMU_PC_FSC_PPN, virt_to_pfn(domain->pgd_root));
> -	ta = FIELD_PREP(RISCV_IOMMU_PC_TA_PSCID, domain->pscid) |
> -	     RISCV_IOMMU_PC_TA_V;
> +	dc.fsc = FIELD_PREP(RISCV_IOMMU_PC_FSC_MODE, domain->pgd_mode) |
> +		 FIELD_PREP(RISCV_IOMMU_PC_FSC_PPN, virt_to_pfn(domain->pgd_root));
> +	dc.ta = FIELD_PREP(RISCV_IOMMU_PC_TA_PSCID, domain->pscid) |
> +			   RISCV_IOMMU_PC_TA_V;
>   
>   	if (riscv_iommu_bond_link(domain, dev))
>   		return -ENOMEM;
>   
> -	riscv_iommu_iodir_update(iommu, dev, fsc, ta);
> +	riscv_iommu_iodir_update(iommu, dev, &dc);
>   	riscv_iommu_bond_unlink(info->domain, dev);
>   	info->domain = domain;
>   
> @@ -1408,9 +1408,12 @@ static int riscv_iommu_attach_blocking_domain(struct iommu_domain *iommu_domain,
>   {
>   	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
>   	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
> +	struct riscv_iommu_dc dc = {0};
> +
> +	dc.fsc = RISCV_IOMMU_FSC_BARE;
>   
>   	/* Make device context invalid, translation requests will fault w/ #258 */
> -	riscv_iommu_iodir_update(iommu, dev, RISCV_IOMMU_FSC_BARE, 0);
> +	riscv_iommu_iodir_update(iommu, dev, &dc);
>   	riscv_iommu_bond_unlink(info->domain, dev);
>   	info->domain = NULL;
>   
> @@ -1429,8 +1432,12 @@ static int riscv_iommu_attach_identity_domain(struct iommu_domain *iommu_domain,
>   {
>   	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
>   	struct riscv_iommu_info *info = dev_iommu_priv_get(dev);
> +	struct riscv_iommu_dc dc = {0};
> +
> +	dc.fsc = RISCV_IOMMU_FSC_BARE;
> +	dc.ta = RISCV_IOMMU_PC_TA_V;
>   
> -	riscv_iommu_iodir_update(iommu, dev, RISCV_IOMMU_FSC_BARE, RISCV_IOMMU_PC_TA_V);
> +	riscv_iommu_iodir_update(iommu, dev, &dc);
>   	riscv_iommu_bond_unlink(info->domain, dev);
>   	info->domain = NULL;
>