linux-kernel - Re: [PATCH 5/5] drm/msm/a6xx: Add support for using system cache(LLC)

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Date:   Thu, 19 Dec 2019 13:10:41 -0700
From:   Jordan Crouse <jcrouse@...eaurora.org>
To:     Sharat Masetty <smasetty@...eaurora.org>,
        freedreno@...ts.freedesktop.org, dri-devel@...edesktop.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        will@...nel.org, robin.murphy@....com, joro@...tes.org,
        iommu@...ts.linux-foundation.org, saiprakash.ranjan@...eaurora.org
Subject: Re: [PATCH 5/5] drm/msm/a6xx: Add support for using system cache(LLC)

On Thu, Dec 19, 2019 at 12:58:15PM -0700, Jordan Crouse wrote:
> On Thu, Dec 19, 2019 at 06:44:46PM +0530, Sharat Masetty wrote:


<snip>

> > +
> > +	/*
> > +	 * CNTL1 is used to specify SCID for (CP, TP, VFD, CCU and UBWC
> > +	 * FLAG cache) GPU blocks. This value will be passed along with
> > +	 * the address for any memory transaction from GPU to identify
> > +	 * the sub-cache for that transaction.
> > +	 */
> > +	if (!IS_ERR(llc->gpu_llc_slice)) {
> > +		u32 gpu_scid = llcc_get_slice_id(llc->gpu_llc_slice);
> > +		int i;
> > +
> > +		for (i = 0; i < A6XX_LLC_NUM_GPU_SCIDS; i++)
> > +			llc->cntl1_regval |=
> > +				gpu_scid << (A6XX_GPU_LLC_SCID_NUM_BITS * i);
> 
> As above, i'm not sure a loop is better than just:
> 
> gpu_scid &= 0x1f;
> 
> llc->cntl1_regval = (gpu_scid << 0) || (gpu_scid << 5) | (gpu_scid << 10)
>  | (gpu_scid << 15) | (gpu_scid << 20);
> 
> And I'm not even sure we need do this math here in the first place.

One more question - can you get a valid slice id before activation?

<snip>

Jordan

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