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Message-ID: <20180809145206.GA26588@ulmo>
Date: Thu, 9 Aug 2018 16:52:06 +0200
From: Thierry Reding <thierry.reding@...il.com>
To: Dmitry Osipenko <digetx@...il.com>
Cc: Joerg Roedel <joro@...tes.org>,
Robin Murphy <robin.murphy@....com>,
Jonathan Hunter <jonathanh@...dia.com>,
iommu@...ts.linux-foundation.org, linux-tegra@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/8] iommu/tegra: gart: Provide access to Memory
Controller driver
On Thu, Aug 09, 2018 at 05:22:59PM +0300, Dmitry Osipenko wrote:
> On Thursday, 9 August 2018 16:59:24 MSK Thierry Reding wrote:
> > On Thu, Aug 09, 2018 at 02:39:03PM +0300, Dmitry Osipenko wrote:
> > > On Thursday, 9 August 2018 14:17:46 MSK Thierry Reding wrote:
> > > > On Sat, Aug 04, 2018 at 05:29:57PM +0300, Dmitry Osipenko wrote:
> > > > > GART contain registers needed by the Memory Controller driver, provide
> > > > > access to the MC driver by utilizing its GART-integration facility.
> > > > >
> > > > > Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> > > > > ---
> > > > >
> > > > > drivers/iommu/tegra-gart.c | 23 +++++++++++++++++++++++
> > > > > 1 file changed, 23 insertions(+)
> > > > >
> > > > > diff --git a/drivers/iommu/tegra-gart.c b/drivers/iommu/tegra-gart.c
> > > > > index a004f6da35f2..f8b653e25914 100644
> > > > > --- a/drivers/iommu/tegra-gart.c
> > > > > +++ b/drivers/iommu/tegra-gart.c
> > > > > @@ -31,6 +31,8 @@
> > > > >
> > > > > #include <linux/iommu.h>
> > > > > #include <linux/of.h>
> > > > >
> > > > > +#include <soc/tegra/mc.h>
> > > > > +
> > > > >
> > > > > #include <asm/cacheflush.h>
> > > > >
> > > > > /* bitmap of the page sizes currently supported */
> > > > >
> > > > > @@ -41,6 +43,8 @@
> > > > >
> > > > > #define GART_ENTRY_ADDR (0x28 - GART_REG_BASE)
> > > > > #define GART_ENTRY_DATA (0x2c - GART_REG_BASE)
> > > > > #define GART_ENTRY_PHYS_ADDR_VALID (1 << 31)
> > > > >
> > > > > +#define GART_ERROR_REQ (0x30 - GART_REG_BASE)
> > > > > +#define GART_ERROR_ADDR (0x34 - GART_REG_BASE)
> > > > >
> > > > > #define GART_PAGE_SHIFT 12
> > > > > #define GART_PAGE_SIZE (1 << GART_PAGE_SHIFT)
> > > > >
> > > > > @@ -63,6 +67,8 @@ struct gart_device {
> > > > >
> > > > > struct device *dev;
> > > > >
> > > > > struct iommu_device iommu; /* IOMMU Core handle */
> > > > >
> > > > > +
> > > > > + struct tegra_mc_gart_handle mc_gart_handle;
> > > > >
> > > > > };
> > > > >
> > > > > struct gart_domain {
> > > > >
> > > > > @@ -408,6 +414,20 @@ static int tegra_gart_resume(struct device *dev)
> > > > >
> > > > > return 0;
> > > > >
> > > > > }
> > > > >
> > > > > +static u32 tegra_gart_error_addr(struct tegra_mc_gart_handle *handle)
> > > > > +{
> > > > > + struct gart_device *gart = container_of(handle, struct
> gart_device,
> > > > > + mc_gart_handle);
> > > > > + return readl_relaxed(gart->regs + GART_ERROR_ADDR);
> > > > > +}
> > > > > +
> > > > > +static u32 tegra_gart_error_req(struct tegra_mc_gart_handle *handle)
> > > > > +{
> > > > > + struct gart_device *gart = container_of(handle, struct
> gart_device,
> > > > > + mc_gart_handle);
> > > > > + return readl_relaxed(gart->regs + GART_ERROR_REQ);
> > > > > +}
> > > > > +
> > > > >
> > > > > static int tegra_gart_probe(struct platform_device *pdev)
> > > > > {
> > > > >
> > > > > struct gart_device *gart;
> > > > >
> > > > > @@ -464,6 +484,8 @@ static int tegra_gart_probe(struct platform_device
> > > > > *pdev)>
> > > > >
> > > > > gart->regs = gart_regs;
> > > > > gart->iovmm_base = (dma_addr_t)res_remap->start;
> > > > > gart->page_count = (resource_size(res_remap) >> GART_PAGE_SHIFT);
> > > > >
> > > > > + gart->mc_gart_handle.error_addr = tegra_gart_error_addr;
> > > > > + gart->mc_gart_handle.error_req = tegra_gart_error_req;
> > > > >
> > > > > gart->savedata = vmalloc(array_size(sizeof(u32), gart->page_count));
> > > > > if (!gart->savedata) {
> > > > >
> > > > > @@ -475,6 +497,7 @@ static int tegra_gart_probe(struct platform_device
> > > > > *pdev)>
> > > > >
> > > > > do_gart_setup(gart, NULL);
> > > > >
> > > > > gart_handle = gart;
> > > > >
> > > > > + tegra_mc_register_gart(&gart->mc_gart_handle);
> > > > >
> > > > > return 0;
> > > > >
> > > > > }
> > > >
> > > > I see now why you've did it this way. We have separate devices unlike
> > > > with SMMU where it is properly modeled as part of the memory controller.
> > > > I think we should consider breaking ABI at this point and properly merge
> > > > both the memory controller and GART nodes. There's really no reason why
> > > > they should be separate and we're jumping through multiple hoops to do
> > > > what we need to do just because a few years back we made a mistake.
> > > >
> > > > I know we're technically not supposed to break the DT ABI, but I think
> > > > in this particular case we can make a good case for it. The current DT
> > > > bindings are plainly broken, and obviously so. Also, we don't currently
> > > > use the GART upstream for anything, so we can't break any existing
> > > > systems either.
> > >
> > > IIUC, that will require to break the stable DT ABI of the tegra20-mc,
> > > which is working fine and does its job. I'm personally not seeing the
> > > slight lameness of the current DT as a good excuse to break the ABI.
> > > Let's then break DT ABI on all Tegra's and convert them all to genpd and
> > > other goodies like assigned clock parents and clock rate.
> >
> > genpd and assigned clocks are complementary, they can be switched to
> > without breaking ABI.
> >
> > And that's also different from the memory controller on Tegra20 where we
> > just made the mistake of describing what is effectively one device as
> > two separate devices. From what I can tell, the only reason this was
> > done was because it mapped better to the Linux driver model where there
> > is a framework to represent an IOMMU and a misunderstanding of how to
> > work with the driver model and device tree.
> >
> > As such, I would describe it as more of a bug in the DT that should be
> > fixed rather than breaking the ABI.
> >
> > And, like I said, we are in the somewhat fortunate situation that we
> > don't actively use the GART, at least in upstream, yet. So even if we
> > break ABI, nobody will notice anyway. Those are about as good pre-
> > conditions as you're going to get for fixing ABI.
>
> Please tell exactly what you're suggesting.
>
> Current DT:
>
> mc: memory-controller@...0f000 {
> compatible = "nvidia,tegra20-mc";
> reg = <0x7000f000 0x024
> 0x7000f03c 0x3c4>;
> interrupts = <GIC_SPI 77 IRQ_TYPE_LEVEL_HIGH>;
> #reset-cells = <1>;
> };
>
> gart: iommu@...0f024 {
> compatible = "nvidia,tegra20-gart";
> reg = <0x7000f024 0x00000018 /* controller registers */
> 0x58000000 0x02000000>; /* GART aperture */
> #iommu-cells = <0>;
> };
>
>
>
> Variant 1 (break MC ABI):
>
> mc: memory-controller@...0f000 {
> compatible = "nvidia,tegra20-mc";
> reg = <0x7000f000 0x400 /* controller registers */
> 0x58000000 0x02000000>; /* GART aperture */
> interrupts = <GIC_SPI 77 IRQ_TYPE_LEVEL_HIGH>;
> #reset-cells = <1>;
> #iommu-cells = <0>;
> };
This is the variant that I would prefer.
Thierry
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