linux-kernel - Re: [PATCH 2/2] iommu: mtk_iommu: Add support for MT6795 Helio X10 M4Us

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Message-ID: <9a67d3e8-8840-03b1-aec8-5a218e810eae@collabora.com>
Date:   Tue, 17 May 2022 11:26:47 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>
Cc:     joro@...tes.org, will@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, matthias.bgg@...il.com,
        iommu@...ts.linux-foundation.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        konrad.dybcio@...ainline.org, marijn.suijten@...ainline.org,
        martin.botka@...ainline.org, ~postmarketos/upstreaming@...ts.sr.ht,
        phone-devel@...r.kernel.org, paul.bouchara@...ainline.org,
        yf.wang@...iatek.com, mingyuan.ma@...iatek.com
Subject: Re: [PATCH 2/2] iommu: mtk_iommu: Add support for MT6795 Helio X10
 M4Us

Il 17/05/22 11:08, Yong Wu ha scritto:
> On Fri, 2022-05-13 at 17:14 +0200, AngeloGioacchino Del Regno wrote:
>> Add support for the M4Us found in the MT6795 Helio X10 SoC.
>>
>> Signed-off-by: AngeloGioacchino Del Regno <
>> angelogioacchino.delregno@...labora.com>
>> ---
>>   drivers/iommu/mtk_iommu.c | 20 +++++++++++++++++++-
>>   1 file changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
>> index 71b2ace74cd6..3d802dd3f377 100644
>> --- a/drivers/iommu/mtk_iommu.c
>> +++ b/drivers/iommu/mtk_iommu.c
>> @@ -157,6 +157,7 @@
>>   enum mtk_iommu_plat {
>>   	M4U_MT2712,
>>   	M4U_MT6779,
>> +	M4U_MT6795,
>>   	M4U_MT8167,
>>   	M4U_MT8173,
>>   	M4U_MT8183,
>> @@ -953,7 +954,8 @@ static int mtk_iommu_hw_init(const struct
>> mtk_iommu_data *data, unsigned int ban
>>   	 * Global control settings are in bank0. May re-init these
>> global registers
>>   	 * since no sure if there is bank0 consumers.
>>   	 */
>> -	if (data->plat_data->m4u_plat == M4U_MT8173) {
>> +	if (data->plat_data->m4u_plat == M4U_MT6795 ||
>> +	    data->plat_data->m4u_plat == M4U_MT8173) {
>>   		regval = F_MMU_PREFETCH_RT_REPLACE_MOD |
>>   			 F_MMU_TF_PROT_TO_PROGRAM_ADDR_MT8173;
>>   	} else {
>> @@ -1138,6 +1140,9 @@ static int mtk_iommu_probe(struct
>> platform_device *pdev)
>>   		case M4U_MT2712:
>>   			p = "mediatek,mt2712-infracfg";
>>   			break;
>> +		case M4U_MT6795:
>> +			p = "mediatek,mt6795-infracfg";
>> +			break;
>>   		case M4U_MT8173:
>>   			p = "mediatek,mt8173-infracfg";
>>   			break;
>> @@ -1404,6 +1409,18 @@ static const struct mtk_iommu_plat_data
>> mt6779_data = {
>>   	.larbid_remap  = {{0}, {1}, {2}, {3}, {5}, {7, 8}, {10}, {9}},
>>   };
>>   
>> +static const struct mtk_iommu_plat_data mt6795_data = {
>> +	.m4u_plat     = M4U_MT6795,
>> +	.flags	      = HAS_4GB_MODE | HAS_BCLK | RESET_AXI |
>> +			HAS_LEGACY_IVRP_PADDR | MTK_IOMMU_TYPE_MM,
>> +	.inv_sel_reg  = REG_MMU_INV_SEL_GEN1,
>> +	.banks_num    = 1,
>> +	.banks_enable = {true},
>> +	.iova_region  = single_domain,
>> +	.iova_region_nr = ARRAY_SIZE(single_domain),
>> +	.larbid_remap = {{0}, {1}, {2}, {3}, {4}}, /* Linear mapping.
>> */
>> +};
> 
> This is nearly same with mt8173_data. mt8173 has one more larb than
> mt6795, its larbid_remap is also ok for mt6795.
> 

I think that we should be explicit about the larbid_remap property,
since mt6795 has one less larb, we should explicitly say that like
I did there... that's only for human readability I admit ... but,
still, I wouldn't want to see people thinking that MT6795 has 6 LARBs
because they've read that larbid_remap having 6 entries.

> thus it looks we could use mt8173 as the backward compatible.
>      compatible = "mediatek,mt6795-m4u",
>                   "mediatek,mt8173-m4u";
> 
> After this, the only thing is about "mediatek,mt6795-infracfg". we have
> to try again with mediatek,mt6795-infracfg after mediatek,mt8173-
> infracfg fail. I think we should allow the backward case in 4GB mode
> judgment if we have.
> 
> What's your opinion? or some other suggestion?
> Thanks.

I know, I may have a plan for that, but I wanted to have a good reason to
propose such a thing, as if it's just about two SoCs needing that, there
would be no good reason to get things done differently.

...so, in order to provide a good cleanup, we have two possible roads to
follow here: either we add a generic "mediatek,infracfg" compatible to the
infra node (but I don't like that), or we can do it like it was previously
done in mtk-pm-domains.c (I prefer that approach):

iommu: iommu@...ewhere {
	... something ...
	mediatek,infracfg = <&infracfg>;
};

infracfg = syscon_regmap_lookup_by_compatible(node, "mediatek,infracfg");
if (IS_ERR(infracfg)) {
	/* try with the older way */
	switch (...) {
	case .... p = "mediatek,mt2712-infracfg";
	... blah blah ...
	}
	/* legacy also failed, ouch! */
	if (IS_ERR(infracfg))
		return PTR_ERR(infracfg);
}

ret = regmap_read ... etc etc etc

Cheers,
Angelo