Re: [PATCH v2 2/2] memory: tegra: Introduce memory client hot reset API

[Thierry Reding]

On Mon, Feb 12, 2018 at 08:06:31PM +0300, Dmitry Osipenko wrote:
> In order to reset busy HW properly, memory controller needs to be
> involved, otherwise it possible to get corrupted memory if HW was reset
> during DMA. Introduce memory client 'hot reset' API that will be used
> for resetting busy HW. The primary users are memory clients related to
> video (decoder/encoder/camera) and graphics (2d/3d).
> 
> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> ---
>  drivers/memory/tegra/mc.c       | 249 ++++++++++++++++++++++++++++++++++++++++
>  drivers/memory/tegra/tegra114.c |  25 ++++
>  drivers/memory/tegra/tegra124.c |  32 ++++++
>  drivers/memory/tegra/tegra20.c  |  23 ++++
>  drivers/memory/tegra/tegra210.c |  27 +++++
>  drivers/memory/tegra/tegra30.c  |  25 ++++
>  include/soc/tegra/mc.h          |  77 +++++++++++++
>  7 files changed, 458 insertions(+)

As discussed on IRC, I typed up a variant of this in an attempt to fix
an unrelated bug report. The code is here:

	https://github.com/thierryreding/linux/commit/e104e703cb75dfe742b2e051194a0af8ddefcd03

I think we can make this without adding a custom API. The reset control
API should work just fine. The above version doesn't take into account
some of Tegra20's quirks, but I think it should still work for Tegra20
with just slightly different implementations for ->assert() and
->deassert().

A couple of more specific comments below.

> diff --git a/drivers/memory/tegra/mc.c b/drivers/memory/tegra/mc.c
> index 187a9005351b..9838f588d64d 100644
> --- a/drivers/memory/tegra/mc.c
> +++ b/drivers/memory/tegra/mc.c
> @@ -7,11 +7,13 @@
>   */
>  
>  #include <linux/clk.h>
> +#include <linux/delay.h>
>  #include <linux/interrupt.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/platform_device.h>
> +#include <linux/reset.h>
>  #include <linux/slab.h>
>  #include <linux/sort.h>
>  
> @@ -81,6 +83,172 @@ static const struct of_device_id tegra_mc_of_match[] = {
>  };
>  MODULE_DEVICE_TABLE(of, tegra_mc_of_match);
>  
> +static int terga_mc_flush_dma(struct tegra_mc *mc, unsigned int id)
> +{
> +	unsigned int hw_id = mc->soc->modules[id].hw_id;
> +	u32 value, reg_poll = mc->soc->reg_client_flush_status;
> +	int retries = 3;
> +
> +	value = mc_readl(mc, mc->soc->reg_client_ctrl);
> +
> +	if (mc->soc->tegra20)
> +		value &= ~BIT(hw_id);
> +	else
> +		value |= BIT(hw_id);
> +
> +	/* block clients DMA requests */
> +	mc_writel(mc, value, mc->soc->reg_client_ctrl);
> +
> +	/* wait for completion of the outstanding DMA requests */
> +	if (mc->soc->tegra20) {
> +		while (mc_readl(mc, reg_poll + hw_id * sizeof(u32)) != 0) {
> +			if (!retries--)
> +				return -EBUSY;
> +
> +			usleep_range(1000, 2000);
> +		}
> +	} else {
> +		while ((mc_readl(mc, reg_poll) & BIT(hw_id)) == 0) {
> +			if (!retries--)
> +				return -EBUSY;
> +
> +			usleep_range(1000, 2000);
> +		}
> +	}
> +
> +	return 0;
> +}

I think this suffers from too much unification. The programming model is
too different to stash this into a single function implementation and as
a result this becomes very difficult to read. In my experience it's more
readable to split this into separate implementations and pass around
pointers to them.

> +
> +static int terga_mc_unblock_dma(struct tegra_mc *mc, unsigned int id)
> +{
> +	unsigned int hw_id = mc->soc->modules[id].hw_id;
> +	u32 value;
> +
> +	value = mc_readl(mc, mc->soc->reg_client_ctrl);
> +
> +	if (mc->soc->tegra20)
> +		value |= BIT(hw_id);
> +	else
> +		value &= ~BIT(hw_id);
> +
> +	mc_writel(mc, value, mc->soc->reg_client_ctrl);
> +
> +	return 0;
> +}
> +
> +static int terga_mc_hotreset_assert(struct tegra_mc *mc, unsigned int id)
> +{
> +	unsigned int hw_id = mc->soc->modules[id].hw_id;
> +	u32 value;
> +
> +	if (mc->soc->tegra20) {
> +		value = mc_readl(mc, mc->soc->reg_client_hotresetn);
> +
> +		mc_writel(mc, value & ~BIT(hw_id),
> +			  mc->soc->reg_client_hotresetn);
> +	}
> +
> +	return 0;
> +}
> +
> +static int terga_mc_hotreset_deassert(struct tegra_mc *mc, unsigned int id)
> +{
> +	unsigned int hw_id = mc->soc->modules[id].hw_id;
> +	u32 value;
> +
> +	if (mc->soc->tegra20) {
> +		value = mc_readl(mc, mc->soc->reg_client_hotresetn);
> +
> +		mc_writel(mc, value | BIT(hw_id),
> +			  mc->soc->reg_client_hotresetn);
> +	}
> +
> +	return 0;
> +}

The same goes for these. I think we can do this much more easily by
providing reset controller API ->assert() and ->deassert()
implementations for Tegra20 and Tegra30+, and then register the reset
controller device using the ops stored in the MC SoC structure.

> +static int tegra_mc_hot_reset_assert(struct tegra_mc *mc, unsigned int id,
> +				     struct reset_control *rst)
> +{
> +	int err;
> +
> +	/*
> +	 * Block clients DMA requests and wait for completion of the
> +	 * outstanding requests.
> +	 */
> +	err = terga_mc_flush_dma(mc, id);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to flush DMA: %d\n", err);
> +		return err;
> +	}
> +
> +	/* put in reset HW that corresponds to the memory client */
> +	err = reset_control_assert(rst);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to assert HW reset: %d\n", err);
> +		return err;
> +	}
> +
> +	/* clear the client requests sitting before arbitration */
> +	err = terga_mc_hotreset_assert(mc, id);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to hot reset client: %d\n", err);
> +		return err;
> +	}
> +
> +	return 0;
> +}

This is very strictly according to the TRM, but I don't see a reason why
you couldn't stash the DMA blocking and the hot reset into a ->assert()
implementation...

> +
> +static int tegra_mc_hot_reset_deassert(struct tegra_mc *mc, unsigned int id,
> +				       struct reset_control *rst)
> +{
> +	int err;
> +
> +	/* take out client from hot reset */
> +	err = terga_mc_hotreset_deassert(mc, id);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to deassert hot reset: %d\n", err);
> +		return err;
> +	}
> +
> +	/* take out from reset corresponding clients HW */
> +	err = reset_control_deassert(rst);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to deassert HW reset: %d\n", err);
> +		return err;
> +	}
> +
> +	/* allow new DMA requests to proceed to arbitration */
> +	err = terga_mc_unblock_dma(mc, id);
> +	if (err) {
> +		dev_err(mc->dev, "Failed to unblock client: %d\n", err);
> +		return err;
> +	}
> +
> +	return 0;
> +}

... and the hot reset deassertion and the DMA unblocking into a
->deassert() implementation.

I think the important part is that DMA is blocked and the requests are
cleared before the module reset, and similarily that the hot reset is
released and DMA is unblocked after the module reset.

> +
> +static int tegra_mc_hot_reset(struct tegra_mc *mc, unsigned int id,
> +			      struct reset_control *rst, unsigned long usecs)
> +{
> +	int err;
> +
> +	err = tegra_mc_hot_reset_assert(mc, id, rst);
> +	if (err)
> +		return err;
> +
> +	/* make sure that reset is propagated */
> +	if (usecs < 15)
> +		udelay(usecs);
> +	else
> +		usleep_range(usecs, usecs + 500);
> +
> +	err = tegra_mc_hot_reset_deassert(mc, id, rst);
> +	if (err)
> +		return err;
> +
> +	return 0;
> +}

Do you really need this helper? It seems like a marginal gain in terms
of boilerplate while obviously some (or maybe even most?) drivers can't
use this because they need more explicit control over the sequence.

The only case where I could see this be useful is during some error
recovery mechanism, in which case perhaps a runtime suspend/resume might
be more useful.

> +
>  static int tegra_mc_setup_latency_allowance(struct tegra_mc *mc)
>  {
>  	unsigned long long tick;
> @@ -416,6 +584,7 @@ static int tegra_mc_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	platform_set_drvdata(pdev, mc);
> +	mutex_init(&mc->lock);
>  	mc->soc = match->data;
>  	mc->dev = &pdev->dev;
>  
> @@ -499,6 +668,86 @@ static struct platform_driver tegra_mc_driver = {
>  	.probe = tegra_mc_probe,
>  };
>  
> +static int tegra_mc_match(struct device *dev, void *data)
> +{
> +	return of_match_node(tegra_mc_of_match, dev->of_node) != NULL;
> +}
> +
> +static struct tegra_mc *tegra_mc_find_device(void)
> +{
> +	struct device *dev;
> +
> +	dev = driver_find_device(&tegra_mc_driver.driver, NULL, NULL,
> +				 tegra_mc_match);
> +	if (!dev)
> +		return NULL;
> +
> +	return dev_get_drvdata(dev);
> +}

Another benefit of the reset controller API is that you don't have to
look up the MC device like this. Instead you can just upcast the pointer
to the reset controller device.

> +
> +int tegra_memory_client_hot_reset(unsigned int id, struct reset_control *rst,
> +				  unsigned long usecs)
> +{
> +	struct tegra_mc *mc;
> +	int ret;
> +
> +	mc = tegra_mc_find_device();
> +	if (!mc)
> +		return -ENODEV;
> +
> +	if (id >= mc->soc->num_modules || !mc->soc->modules[id].valid)
> +		return -EINVAL;

One of the problems with sparse arrays is that you need to explicitly
mark each of the entries as valid. This is error prone and tedious in
my opinion.

> +
> +	mutex_lock(&mc->lock);
> +	ret = tegra_mc_hot_reset(mc, id, rst, usecs);
> +	mutex_unlock(&mc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(tegra_memory_client_hot_reset);
> +
> +int tegra_memory_client_hot_reset_assert(unsigned int id,
> +					 struct reset_control *rst)
> +{
> +	struct tegra_mc *mc;
> +	int ret;
> +
> +	mc = tegra_mc_find_device();
> +	if (!mc)
> +		return -ENODEV;
> +
> +	if (id >= mc->soc->num_modules || !mc->soc->modules[id].valid)
> +		return -EINVAL;
> +
> +	mutex_lock(&mc->lock);
> +	ret = tegra_mc_hot_reset_assert(mc, id, rst);
> +	mutex_unlock(&mc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(tegra_memory_client_hot_reset_assert);
> +
> +int tegra_memory_client_hot_reset_deassert(unsigned int id,
> +					   struct reset_control *rst)
> +{
> +	struct tegra_mc *mc;
> +	int ret;
> +
> +	mc = tegra_mc_find_device();
> +	if (!mc)
> +		return -ENODEV;
> +
> +	if (id >= mc->soc->num_modules || !mc->soc->modules[id].valid)
> +		return -EINVAL;

There's a lot of repetition in the code here. If you look at my
prototype, I think this is simpler to deal with if you get a reference
to the reset and then just use it. All of the special case handling is
done in the lookup function, and then you get back NULL or a valid
pointer that you can immediately use.

> +
> +	mutex_lock(&mc->lock);
> +	ret = tegra_mc_hot_reset_deassert(mc, id, rst);
> +	mutex_unlock(&mc->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(tegra_memory_client_hot_reset_deassert);
> +
>  static int tegra_mc_init(void)
>  {
>  	return platform_driver_register(&tegra_mc_driver);
[...]
> diff --git a/drivers/memory/tegra/tegra124.c b/drivers/memory/tegra/tegra124.c
> index 8b6360eabb8a..135012c74358 100644
> --- a/drivers/memory/tegra/tegra124.c
> +++ b/drivers/memory/tegra/tegra124.c
> @@ -1012,6 +1012,30 @@ static const struct tegra_smmu_group_soc tegra124_groups[] = {
>  	},
>  };
>  
> +static const struct tegra_mc_module tegra124_mc_modules[] = {
> +	[TEGRA_MEMORY_CLIENT_AFI]	= { .hw_id =  0, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_AVP]	= { .hw_id =  1, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_DC]	= { .hw_id =  2, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_DCB]	= { .hw_id =  3, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_HOST1X]	= { .hw_id =  6, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_HDA]	= { .hw_id =  7, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_ISP2]	= { .hw_id =  8, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_MPCORE]	= { .hw_id =  9, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_MPCORELP]	= { .hw_id = 10, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_MSENC]	= { .hw_id = 11, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_PPCS]	= { .hw_id = 14, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_SATA]	= { .hw_id = 15, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_VDE]	= { .hw_id = 16, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_VI]	= { .hw_id = 17, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_VIC]	= { .hw_id = 18, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_XUSB_HOST]	= { .hw_id = 19, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_XUSB_DEV]	= { .hw_id = 20, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_TSEC]	= { .hw_id = 22, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_SDMMC1]	= { .hw_id = 29, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_SDMMC2]	= { .hw_id = 30, .valid = true },
> +	[TEGRA_MEMORY_CLIENT_SDMMC3]	= { .hw_id = 31, .valid = true },
> +};

This list is incomplete. The same is true for any later generation.
There are also quite a few holes in them. I think a better use of this
space is to make the array compact and instead have more explicit
information in the array.

> diff --git a/include/soc/tegra/mc.h b/include/soc/tegra/mc.h
> index 6cfc1dfa3a40..2d36db3ac659 100644
> --- a/include/soc/tegra/mc.h
> +++ b/include/soc/tegra/mc.h
> @@ -9,11 +9,13 @@
>  #ifndef __SOC_TEGRA_MC_H__
>  #define __SOC_TEGRA_MC_H__
>  
> +#include <linux/mutex.h>
>  #include <linux/types.h>
>  
>  struct clk;
>  struct device;
>  struct page;
> +struct reset_control;
>  
>  struct tegra_smmu_enable {
>  	unsigned int reg;
> @@ -95,6 +97,11 @@ static inline void tegra_smmu_remove(struct tegra_smmu *smmu)
>  }
>  #endif
>  
> +struct tegra_mc_module {
> +	unsigned int hw_id;
> +	bool valid;
> +};
> +
>  struct tegra_mc_soc {
>  	const struct tegra_mc_client *clients;
>  	unsigned int num_clients;
> @@ -110,6 +117,13 @@ struct tegra_mc_soc {
>  	const struct tegra_smmu_soc *smmu;
>  
>  	bool tegra20;
> +
> +	const struct tegra_mc_module *modules;
> +	unsigned int num_modules;
> +
> +	u32 reg_client_ctrl;
> +	u32 reg_client_hotresetn;
> +	u32 reg_client_flush_status;

That's not enough to cover all clients on Tegra124 and later. We need at
least two registers. I'd also prefer to move away from the assumption
that the ID is somehow linked to the bit position. The ID is in fact
completely arbitrary and in this case only chosen to match the bit
position.

This has multiple disadvantages, some of which I've already listed. One
of them is that we inevitably make arrays sparse as the SoC evolves, so
we need to work around this in code and data tables using a valid flag.
Checking for validity also becomes non-trivial and we move part of that
burden into drivers.

I think a much better and robust solution is to completely separate the
ID from the hardware registers. This is implemented in my prototype on
github. The ID is essentially only used as a way to identify the reset
via device tree. The MC driver will use the ID to look up the reset in
its per-SoC table and will only work with the reset object after that.
The object itself contains all the information needed to program the
registers.

Currently the tables in that implementation don't take into account the
per-client "outstanding requests" registers, but they could be easily
extended to do so.

>  };
>  
>  struct tegra_mc {
> @@ -124,9 +138,72 @@ struct tegra_mc {
>  
>  	struct tegra_mc_timing *timings;
>  	unsigned int num_timings;
> +
> +	struct mutex lock;
>  };
>  
>  void tegra_mc_write_emem_configuration(struct tegra_mc *mc, unsigned long rate);
>  unsigned int tegra_mc_get_emem_device_count(struct tegra_mc *mc);
>  
> +#define TEGRA_MEMORY_CLIENT_AVP		0
> +#define TEGRA_MEMORY_CLIENT_DC		1
> +#define TEGRA_MEMORY_CLIENT_DCB		2
> +#define TEGRA_MEMORY_CLIENT_EPP		3
> +#define TEGRA_MEMORY_CLIENT_2D		4
> +#define TEGRA_MEMORY_CLIENT_HOST1X	5
> +#define TEGRA_MEMORY_CLIENT_ISP		6
> +#define TEGRA_MEMORY_CLIENT_MPCORE	7
> +#define TEGRA_MEMORY_CLIENT_MPCORELP	8
> +#define TEGRA_MEMORY_CLIENT_MPEA	9
> +#define TEGRA_MEMORY_CLIENT_MPEB	10
> +#define TEGRA_MEMORY_CLIENT_MPEC	11
> +#define TEGRA_MEMORY_CLIENT_3D		12
> +#define TEGRA_MEMORY_CLIENT_3D1		13
> +#define TEGRA_MEMORY_CLIENT_PPCS	14
> +#define TEGRA_MEMORY_CLIENT_VDE		15
> +#define TEGRA_MEMORY_CLIENT_VI		16
> +#define TEGRA_MEMORY_CLIENT_AFI		17
> +#define TEGRA_MEMORY_CLIENT_HDA		18
> +#define TEGRA_MEMORY_CLIENT_SATA	19
> +#define TEGRA_MEMORY_CLIENT_MSENC	20
> +#define TEGRA_MEMORY_CLIENT_VIC		21
> +#define TEGRA_MEMORY_CLIENT_XUSB_HOST	22
> +#define TEGRA_MEMORY_CLIENT_XUSB_DEV	23
> +#define TEGRA_MEMORY_CLIENT_TSEC	24
> +#define TEGRA_MEMORY_CLIENT_SDMMC1	25
> +#define TEGRA_MEMORY_CLIENT_SDMMC2	26
> +#define TEGRA_MEMORY_CLIENT_SDMMC3	27
> +#define TEGRA_MEMORY_CLIENT_MAX		TEGRA_MEMORY_CLIENT_SDMMC3
> +
> +#define TEGRA_MEMORY_CLIENT_3D0		TEGRA_MEMORY_CLIENT_3D
> +#define TEGRA_MEMORY_CLIENT_MPE		TEGRA_MEMORY_CLIENT_MPEA
> +#define TEGRA_MEMORY_CLIENT_NVENC	TEGRA_MEMORY_CLIENT_MSENC
> +#define TEGRA_MEMORY_CLIENT_ISP2	TEGRA_MEMORY_CLIENT_ISP
> +
> +#ifdef CONFIG_ARCH_TEGRA
> +int tegra_memory_client_hot_reset(unsigned int id, struct reset_control *rst,
> +				  unsigned long usecs);
> +int tegra_memory_client_hot_reset_assert(unsigned int id,
> +					 struct reset_control *rst);
> +int tegra_memory_client_hot_reset_deassert(unsigned int id,
> +					   struct reset_control *rst);
> +#else

I *really* don't want yet another custom API. We've had a number of
these in the past and it's always been extremely painful to get rid of
them. And we probably won't ever be able to completely get rid of the
powergate API, which means additional headaches everytime we need to
touch code in that area. I don't want to repeat that mistake.

Thierry

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