linux-kernel - Re: [PATCHv5 4/6] drm/msm/a6xx: Add support for using system cache(LLC)

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Date:   Mon, 28 Sep 2020 17:56:55 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Rob Clark <robdclark@...il.com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        freedreno@...ts.freedesktop.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        dri-devel@...ts.freedesktop.org,
        Sharat Masetty <smasetty@...eaurora.org>,
        Jonathan Marek <jonathan@...ek.ca>
Subject: Re: [PATCHv5 4/6] drm/msm/a6xx: Add support for using system
 cache(LLC)

Hi Jordan,

On 2020-09-23 20:33, Jordan Crouse wrote:
> On Tue, Sep 22, 2020 at 11:48:17AM +0530, Sai Prakash Ranjan wrote:
>> From: Sharat Masetty <smasetty@...eaurora.org>
>> 
>> The last level system cache can be partitioned to 32 different
>> slices of which GPU has two slices preallocated. One slice is
>> used for caching GPU buffers and the other slice is used for
>> caching the GPU SMMU pagetables. This talks to the core system
>> cache driver to acquire the slice handles, configure the SCID's
>> to those slices and activates and deactivates the slices upon
>> GPU power collapse and restore.
>> 
>> Some support from the IOMMU driver is also needed to make use
>> of the system cache to set the right TCR attributes. GPU then
>> has the ability to override a few cacheability parameters which
>> it does to override write-allocate to write-no-allocate as the
>> GPU hardware does not benefit much from it.
>> 
>> DOMAIN_ATTR_SYS_CACHE is another domain level attribute used by the
>> IOMMU driver to set the right attributes to cache the hardware
>> pagetables into the system cache.
>> 
>> Signed-off-by: Sharat Masetty <smasetty@...eaurora.org>
>> [saiprakash.ranjan: fix to set attr before device attach to iommu and 
>> rebase]
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> ---
>>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c   | 83 
>> +++++++++++++++++++++++++
>>  drivers/gpu/drm/msm/adreno/a6xx_gpu.h   |  4 ++
>>  drivers/gpu/drm/msm/adreno/adreno_gpu.c | 17 +++++
>>  3 files changed, 104 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c 
>> b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>> index 8915882e4444..151190ff62f7 100644
>> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
>> @@ -8,7 +8,9 @@
>>  #include "a6xx_gpu.h"
>>  #include "a6xx_gmu.xml.h"
>> 
>> +#include <linux/bitfield.h>
>>  #include <linux/devfreq.h>
>> +#include <linux/soc/qcom/llcc-qcom.h>
>> 
>>  #define GPU_PAS_ID 13
>> 
>> @@ -1022,6 +1024,79 @@ static irqreturn_t a6xx_irq(struct msm_gpu 
>> *gpu)
>>  	return IRQ_HANDLED;
>>  }
>> 
>> +static void a6xx_llc_rmw(struct a6xx_gpu *a6xx_gpu, u32 reg, u32 
>> mask, u32 or)
>> +{
>> +	return msm_rmw(a6xx_gpu->llc_mmio + (reg << 2), mask, or);
>> +}
>> +
>> +static void a6xx_llc_write(struct a6xx_gpu *a6xx_gpu, u32 reg, u32 
>> value)
>> +{
>> +	return msm_writel(value, a6xx_gpu->llc_mmio + (reg << 2));
>> +}
>> +
>> +static void a6xx_llc_deactivate(struct a6xx_gpu *a6xx_gpu)
>> +{
>> +	llcc_slice_deactivate(a6xx_gpu->llc_slice);
>> +	llcc_slice_deactivate(a6xx_gpu->htw_llc_slice);
>> +}
>> +
>> +static void a6xx_llc_activate(struct a6xx_gpu *a6xx_gpu)
>> +{
>> +	u32 cntl1_regval = 0;
>> +
>> +	if (IS_ERR(a6xx_gpu->llc_mmio))
>> +		return;
>> +
>> +	if (!llcc_slice_activate(a6xx_gpu->llc_slice)) {
>> +		u32 gpu_scid = llcc_get_slice_id(a6xx_gpu->llc_slice);
>> +
>> +		gpu_scid &= 0x1f;
>> +		cntl1_regval = (gpu_scid << 0) | (gpu_scid << 5) | (gpu_scid << 10) 
>> |
>> +			       (gpu_scid << 15) | (gpu_scid << 20);
>> +	}
>> +
>> +	if (!llcc_slice_activate(a6xx_gpu->htw_llc_slice)) {
>> +		u32 gpuhtw_scid = llcc_get_slice_id(a6xx_gpu->htw_llc_slice);
>> +
>> +		gpuhtw_scid &= 0x1f;
>> +		cntl1_regval |= FIELD_PREP(GENMASK(29, 25), gpuhtw_scid);
>> +	}
>> +
>> +	if (cntl1_regval) {
>> +		/*
>> +		 * Program the slice IDs for the various GPU blocks and GPU MMU
>> +		 * pagetables
>> +		 */
>> +		a6xx_llc_write(a6xx_gpu, REG_A6XX_CX_MISC_SYSTEM_CACHE_CNTL_1, 
>> cntl1_regval);
>> +
>> +		/*
>> +		 * Program cacheability overrides to not allocate cache lines on
>> +		 * a write miss
>> +		 */
>> +		a6xx_llc_rmw(a6xx_gpu, REG_A6XX_CX_MISC_SYSTEM_CACHE_CNTL_0, 0xF, 
>> 0x03);
>> +	}
>> +}
> 
> This code has been around long enough that it pre-dates a650. On a650 
> and other
> MMU-500 targets the htw_llc is configured by the firmware and the 
> llc_slice is
> configured in a different register.
> 
> I don't think we need to pause everything and add support for the 
> MMU-500 path,
> but we do need a way to disallow LLCC on affected targets until such 
> time that
> we can get it fixed up.
> 

Thanks for taking a close look, does something like below look ok or 
something
else is needed here?

+         /* Till the time we get in LLCC support for A650 */
+         if (!(info && info->revn == 650))
+                 a6xx_llc_slices_init(pdev, a6xx_gpu);

Thanks,
Sai

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