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

Sai Prakash Ranjan
2020-09-28T12:27:07Z

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@codeaurora.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@codeaurora.org>
>> [saiprakash.ranjan: fix to set attr before device attach to iommu and
>> rebase]
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.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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