Re: [PATCH v2] iommu/mediatek: check 4GB mode by reading infracfg

[Miles Chen <miles.chen@mediatek.com>]

On Tue, 2020-07-21 at 11:10 +0200, David Hildenbrand wrote:
> On 21.07.20 04:16, Miles Chen wrote:
> > In previous discussion [1] and [2], we found that it is risky to
> > use max_pfn or totalram_pages to tell if 4GB mode is enabled.
> > 
> > Check 4GB mode by reading infracfg register, remove the usage
> > of the un-exported symbol max_pfn.
> > 
> > This is a step towards building mtk_iommu as a kernel module.
> > 
> > Change since v1:
> > 1. remove the phandle usage, search for infracfg instead [3]
> > 2. use infracfg instead of infracfg_regmap
> > 3. move infracfg definitaions to linux/soc/mediatek/infracfg.h
> > 4. update enable_4GB only when has_4gb_mode
> 
> Nit: We tend to place such information below the "---" (adding a second
> one) such that this information is discarded when the patch is picked up.

Thanks, I'll add a "---" before the "Change since..." in patch v3.
> 
> > 
> > [1] https://urldefense.com/v3/__https://lkml.org/lkml/2020/6/3/733__;!!CTRNKA9wMg0ARbw!wrP2H0azuZkTHSnM_ETki4kT_FMF0Cl7abQX8tIHX0iTr65JkvMCe4jDt84d_YhBrA$ 
> > [2] https://urldefense.com/v3/__https://lkml.org/lkml/2020/6/4/136__;!!CTRNKA9wMg0ARbw!wrP2H0azuZkTHSnM_ETki4kT_FMF0Cl7abQX8tIHX0iTr65JkvMCe4jDt86IGhmouQ$ 
> > [3] https://urldefense.com/v3/__https://lkml.org/lkml/2020/7/15/1147__;!!CTRNKA9wMg0ARbw!wrP2H0azuZkTHSnM_ETki4kT_FMF0Cl7abQX8tIHX0iTr65JkvMCe4jDt855z4xdqw$ 
> > 
> > Cc: Mike Rapoport <rppt@linux.ibm.com>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: Yong Wu <yong.wu@mediatek.com>
> > Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Yong Wu <yong.wu@mediatek.com>
> > Cc: Chao Hao <chao.hao@mediatek.com>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Matthias Brugger <matthias.bgg@gmail.com>
> > Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> > ---
> >  drivers/iommu/mtk_iommu.c             | 26 +++++++++++++++++++++-----
> >  include/linux/soc/mediatek/infracfg.h |  3 +++
> >  2 files changed, 24 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index 2be96f1cdbd2..16765f532853 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -3,7 +3,6 @@
> >   * Copyright (c) 2015-2016 MediaTek Inc.
> >   * Author: Yong Wu <yong.wu@mediatek.com>
> >   */
> > -#include <linux/memblock.h>
> >  #include <linux/bug.h>
> >  #include <linux/clk.h>
> >  #include <linux/component.h>
> > @@ -15,13 +14,16 @@
> >  #include <linux/iommu.h>
> >  #include <linux/iopoll.h>
> >  #include <linux/list.h>
> > +#include <linux/mfd/syscon.h>
> >  #include <linux/of_address.h>
> >  #include <linux/of_iommu.h>
> >  #include <linux/of_irq.h>
> >  #include <linux/of_platform.h>
> >  #include <linux/platform_device.h>
> > +#include <linux/regmap.h>
> >  #include <linux/slab.h>
> >  #include <linux/spinlock.h>
> > +#include <linux/soc/mediatek/infracfg.h>
> >  #include <asm/barrier.h>
> >  #include <soc/mediatek/smi.h>
> >  
> > @@ -599,8 +601,10 @@ static int mtk_iommu_probe(struct platform_device *pdev)
> >  	struct resource         *res;
> >  	resource_size_t		ioaddr;
> >  	struct component_match  *match = NULL;
> > +	struct regmap		*infracfg;
> >  	void                    *protect;
> >  	int                     i, larb_nr, ret;
> > +	u32			val;
> >  
> >  	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> >  	if (!data)
> > @@ -614,10 +618,22 @@ static int mtk_iommu_probe(struct platform_device *pdev)
> >  		return -ENOMEM;
> >  	data->protect_base = ALIGN(virt_to_phys(protect), MTK_PROTECT_PA_ALIGN);
> >  
> > -	/* Whether the current dram is over 4GB */
> > -	data->enable_4GB = !!(max_pfn > (BIT_ULL(32) >> PAGE_SHIFT));
> > -	if (!data->plat_data->has_4gb_mode)
> > -		data->enable_4GB = false;
> > +	data->enable_4GB = false;
> > +	if (data->plat_data->has_4gb_mode) {
> > +		infracfg = syscon_regmap_lookup_by_compatible(
> > +				"mediatek,mt8173-infracfg");
> > +		if (IS_ERR(infracfg)) {
> > +			infracfg = syscon_regmap_lookup_by_compatible(
> > +					"mediatek,mt2712-infracfg");
> > +			if (IS_ERR(infracfg))
> > +				return PTR_ERR(infracfg);
> > +
> > +		}
> > +		ret = regmap_read(infracfg, REG_INFRA_MISC, &val);
> > +		if (ret)
> > +			return ret;
> > +		data->enable_4GB = !!(val & F_DDR_4GB_SUPPORT_EN);
> 
> (I am absolutely not familiar with syscon_regmap_lookup_by ..., I am
> missing some context, so sorry for the stupid questions)
> 
> Who sets the regmap value and based on what? Who decides that 4GB mode
> is supported or not? And who decides if 4GB mode is *required* or not?
> 

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