linux-kernel - Re: [PATCH v3 1/3] iommu: io-pgtable: Add ARM Mali midgard MMU page table format

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Message-ID: <85471882-3044-eba7-8351-fb01330004d8@arm.com>
Date:   Fri, 5 Apr 2019 11:02:31 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Rob Herring <robh@...nel.org>, dri-devel@...ts.freedesktop.org
Cc:     Lyude Paul <lyude@...hat.com>, Eric Anholt <eric@...olt.net>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Will Deacon <will.deacon@....com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        iommu@...ts.linux-foundation.org,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Daniel Vetter <daniel@...ll.ch>, Sean Paul <sean@...rly.run>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] iommu: io-pgtable: Add ARM Mali midgard MMU page
 table format

On 01/04/2019 20:11, Robin Murphy wrote:
> On 01/04/2019 08:47, Rob Herring wrote:
>> ARM Mali midgard GPU is similar to standard 64-bit stage 1 page 
>> tables, but
>> have a few differences. Add a new format type to represent the format. 
>> The
>> input address size is 48-bits and the output address size is 40-bits (and
>> possibly less?). Note that the later bifrost GPUs follow the standard
>> 64-bit stage 1 format.
>>
>> The differences in the format compared to 64-bit stage 1 format are:
>>
>> The 3rd level page entry bits are 0x1 instead of 0x3 for page entries.
>>
>> The access flags are not read-only and unprivileged, but read and write.
>> This is similar to stage 2 entries, but the memory attributes field 
>> matches
>> stage 1 being an index.
>>
>> The nG bit is not set by the vendor driver. This one didn't seem to 
>> matter,
>> but we'll keep it aligned to the vendor driver.
>>
>> Cc: Will Deacon <will.deacon@....com>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Cc: Joerg Roedel <joro@...tes.org>
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: iommu@...ts.linux-foundation.org
>> Signed-off-by: Rob Herring <robh@...nel.org>
>> ---
>> Please ack this as I need to apply it to the drm-misc tree. Or we need a
>> stable branch with this patch.
> 
> With the diff below squashed in to address my outstanding style nits,
> 
> Acked-by: Robin Murphy <robin.murphy@....com>
> 
> I don't foresee any conflicting io-pgtable changes to prevent this going 
> via DRM, but I'll leave the final say up to Joerg.

Urgh, sorry, turns out I flipped one condition too many there. On 
reflection I may also forget my clever trick in future and inadvertently 
break it, so it probably warrants a comment. Please supersede my 
previous request with the (actually tested) diff below :)

Thanks,
Robin.

----->8-----
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 98551d0cff59..4f7be5a3e19b 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -197,12 +197,13 @@ struct arm_lpae_io_pgtable {

  typedef u64 arm_lpae_iopte;

-static inline bool iopte_leaf(arm_lpae_iopte pte, int l, enum 
io_pgtable_fmt fmt)
+static inline bool iopte_leaf(arm_lpae_iopte pte, int lvl,
+			      enum io_pgtable_fmt fmt)
  {
-	if ((l == (ARM_LPAE_MAX_LEVELS - 1)) && (fmt != ARM_MALI_LPAE))
-		return iopte_type(pte,l) == ARM_LPAE_PTE_TYPE_PAGE;
+	if (lvl == (ARM_LPAE_MAX_LEVELS - 1) && fmt != ARM_MALI_LPAE)
+		return iopte_type(pte, lvl) == ARM_LPAE_PTE_TYPE_PAGE;

-	return iopte_type(pte,l) == ARM_LPAE_PTE_TYPE_BLOCK;
+	return iopte_type(pte, lvl) == ARM_LPAE_PTE_TYPE_BLOCK;
  }

  static arm_lpae_iopte paddr_to_iopte(phys_addr_t paddr,
@@ -310,12 +311,9 @@ static void __arm_lpae_init_pte(struct 
arm_lpae_io_pgtable *data,
  	if (data->iop.cfg.quirks & IO_PGTABLE_QUIRK_ARM_NS)
  		pte |= ARM_LPAE_PTE_NS;

-	if (lvl == ARM_LPAE_MAX_LEVELS - 1) {
-		if (data->iop.fmt == ARM_MALI_LPAE)
-			pte |= ARM_LPAE_PTE_TYPE_BLOCK;
-		else
-			pte |= ARM_LPAE_PTE_TYPE_PAGE;
-	} else
+	if (data->iop.fmt != ARM_MALI_LPAE && lvl == ARM_LPAE_MAX_LEVELS - 1)
+		pte |= ARM_LPAE_PTE_TYPE_PAGE;
+	else
  		pte |= ARM_LPAE_PTE_TYPE_BLOCK;

  	if (data->iop.fmt != ARM_MALI_LPAE)
@@ -452,7 +450,10 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct 
arm_lpae_io_pgtable *data,
  		if (prot & IOMMU_WRITE)
  			pte |= ARM_LPAE_PTE_HAP_WRITE;
  	}
-
+	/*
+	 * Note that this logic is structured to accommodate Mali LPAE
+	 * having stage-1-like attributes but stage-2-like permissions.
+	 */
  	if (data->iop.fmt == ARM_64_LPAE_S2 ||
  	    data->iop.fmt == ARM_32_LPAE_S2) {
  		if (prot & IOMMU_MMIO)