Re: [RFC PATCH 2/2] soc: ti: Add Support for the TI Page-based Address Translator (PAT)

["Andrew F. Davis" <afd@ti.com>]

On 6/18/19 5:07 AM, Tero Kristo wrote:
> On 07/06/2019 22:35, Andrew F. Davis wrote:
>> This patch adds a driver for the Page-based Address Translator (PAT)
>> present on various TI SoCs. A PAT device performs address translation
>> using tables stored in an internal SRAM. Each PAT supports a set number
>> of pages, each occupying a programmable 4KB, 16KB, 64KB, or 1MB of
>> addresses in a window for which an incoming transaction will be
>> translated.
>>
>> Signed-off-by: Andrew F. Davis <afd@ti.com>
>> ---
>>   drivers/soc/ti/Kconfig      |   9 +
>>   drivers/soc/ti/Makefile     |   1 +
>>   drivers/soc/ti/ti-pat.c     | 569 ++++++++++++++++++++++++++++++++++++
>>   include/uapi/linux/ti-pat.h |  44 +++
>>   4 files changed, 623 insertions(+)
>>   create mode 100644 drivers/soc/ti/ti-pat.c
>>   create mode 100644 include/uapi/linux/ti-pat.h
>>
>> diff --git a/drivers/soc/ti/Kconfig b/drivers/soc/ti/Kconfig
>> index f0be35d3dcba..b838ae74d01f 100644
>> --- a/drivers/soc/ti/Kconfig
>> +++ b/drivers/soc/ti/Kconfig
>> @@ -86,4 +86,13 @@ config TI_SCI_INTA_MSI_DOMAIN
>>       help
>>         Driver to enable Interrupt Aggregator specific MSI Domain.
>>   +config TI_PAT
>> +    tristate "TI PAT DMA-BUF exporter"
>> +    select REGMAP
> 
> What is the reasoning for using regmap for internal register access? Why
> not just use direct readl/writel for everything? To me it seems this is
> only used during probe time also...
> 

There are two register spaces, the configuration space, and the actual
translation table data. I use regmap for all the configuration space.
Direct readl/writel would also work, but I prefer regmap as it lets me
work with field names vs using masks and shifts, even if it adds a
little extra code in tables at the top.

>> +    help
>> +      Driver for TI Page-based Address Translator (PAT). This driver
>> +      provides the an API allowing the remapping of a non-contiguous
>> +      DMA-BUF into a contiguous one that is sutable for devices needing
>> +      coniguous memory.
> 
> Minor typo: contiguous.
> 

ACK

>> +
>>   endif # SOC_TI
>> diff --git a/drivers/soc/ti/Makefile b/drivers/soc/ti/Makefile
>> index b3868d392d4f..1369642b40c3 100644
>> --- a/drivers/soc/ti/Makefile
>> +++ b/drivers/soc/ti/Makefile
>> @@ -9,3 +9,4 @@ obj-$(CONFIG_AMX3_PM)            += pm33xx.o
>>   obj-$(CONFIG_WKUP_M3_IPC)        += wkup_m3_ipc.o
>>   obj-$(CONFIG_TI_SCI_PM_DOMAINS)        += ti_sci_pm_domains.o
>>   obj-$(CONFIG_TI_SCI_INTA_MSI_DOMAIN)    += ti_sci_inta_msi.o
>> +obj-$(CONFIG_TI_PAT)            += ti-pat.o
>> diff --git a/drivers/soc/ti/ti-pat.c b/drivers/soc/ti/ti-pat.c
>> new file mode 100644
>> index 000000000000..7359ea0f7ccf
>> --- /dev/null
>> +++ b/drivers/soc/ti/ti-pat.c
>> @@ -0,0 +1,569 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * TI PAT mapped DMA-BUF memory re-exporter
>> + *
>> + * Copyright (C) 2018-2019 Texas Instruments Incorporated -
>> http://www.ti.com/
>> + *    Andrew F. Davis <afd@ti.com>
>> + */
>> +
>> +#include <linux/fs.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/mod_devicetable.h>
>> +#include <linux/uaccess.h>
>> +#include <linux/miscdevice.h>
>> +#include <linux/regmap.h>
>> +#include <linux/dma-buf.h>
>> +#include <linux/genalloc.h>
>> +#include <linux/vmalloc.h>
>> +#include <linux/slab.h>
>> +
>> +#include <linux/ti-pat.h>
>> +
>> +#define TI_PAT_DRIVER_NAME    "ti-pat"
> 
> Why do you have a define for this seeing it is only used in single
> location?
> 

Just habit when starting a driver, but you are right it is not needed here.

>> +
>> +/* TI PAT MMRS registers */
>> +#define TI_PAT_MMRS_PID        0x0 /* Revision Register */
>> +#define TI_PAT_MMRS_CONFIG    0x4 /* Config Register */
>> +#define TI_PAT_MMRS_CONTROL    0x10 /* Control Register */
>> +
>> +/* TI PAT CONTROL register field values */
>> +#define TI_PAT_CONTROL_ARB_MODE_UF    0x0 /* Updates first */
>> +#define TI_PAT_CONTROL_ARB_MODE_RR    0x2 /* Round-robin */
>> +
>> +#define TI_PAT_CONTROL_PAGE_SIZE_4KB    0x0
>> +#define TI_PAT_CONTROL_PAGE_SIZE_16KB    0x1
>> +#define TI_PAT_CONTROL_PAGE_SIZE_64KB    0x2
>> +#define TI_PAT_CONTROL_PAGE_SIZE_1MB    0x3
>> +
>> +static unsigned int ti_pat_page_sizes[] = {
>> +    [TI_PAT_CONTROL_PAGE_SIZE_4KB]  = 4 * 1024,
>> +    [TI_PAT_CONTROL_PAGE_SIZE_16KB] = 16 * 1024,
>> +    [TI_PAT_CONTROL_PAGE_SIZE_64KB] = 64 * 1024,
>> +    [TI_PAT_CONTROL_PAGE_SIZE_1MB]  = 1024 * 1024,
>> +};
>> +
>> +enum ti_pat_mmrs_fields {
>> +    /* Revision */
>> +    F_PID_MAJOR,
>> +    F_PID_MINOR,
>> +
>> +    /* Controls */
>> +    F_CONTROL_ARB_MODE,
>> +    F_CONTROL_PAGE_SIZE,
>> +    F_CONTROL_REPLACE_OID_EN,
>> +    F_CONTROL_EN,
>> +
>> +    /* sentinel */
>> +    F_MAX_FIELDS
>> +};
>> +
>> +static const struct reg_field ti_pat_mmrs_reg_fields[] = {
>> +    /* Revision */
>> +    [F_PID_MAJOR]            = REG_FIELD(TI_PAT_MMRS_PID, 8, 10),
>> +    [F_PID_MINOR]            = REG_FIELD(TI_PAT_MMRS_PID, 0, 5),
>> +    /* Controls */
>> +    [F_CONTROL_ARB_MODE]        = REG_FIELD(TI_PAT_MMRS_CONTROL, 6, 7),
>> +    [F_CONTROL_PAGE_SIZE]        = REG_FIELD(TI_PAT_MMRS_CONTROL, 4, 5),
>> +    [F_CONTROL_REPLACE_OID_EN]    = REG_FIELD(TI_PAT_MMRS_CONTROL, 1,
>> 1),
>> +    [F_CONTROL_EN]            = REG_FIELD(TI_PAT_MMRS_CONTROL, 0, 0),
>> +};
>> +
>> +/**
>> + * struct ti_pat_data - PAT device instance data
>> + * @dev: PAT device structure
>> + * @mdev: misc device
>> + * @mmrs_map: Register map of MMRS region
>> + * @table_base: Base address of TABLE region
> 
> Please add kerneldoc comments for all fields.
> 

Will add.

>> + */
>> +struct ti_pat_data {
>> +    struct device *dev;
>> +    struct miscdevice mdev;
>> +    struct regmap *mmrs_map;
>> +    struct regmap_field *mmrs_fields[F_MAX_FIELDS];
>> +    void __iomem *table_base;
>> +    unsigned int page_count;
>> +    unsigned int page_size;
>> +    phys_addr_t window_base;
>> +    struct gen_pool *pool;
>> +};
>> +
> 
> Kerneldoc comments for below structs would be also useful, especially
> for ti_pat_buffer.
> 

Will add.

>> +struct ti_pat_dma_buf_attachment {
>> +    struct device *dev;
>> +    struct sg_table *table;
>> +    struct ti_pat_buffer *buffer;
>> +    struct list_head list;
>> +};
>> +
>> +struct ti_pat_buffer {
>> +    struct ti_pat_data *pat;
>> +    struct dma_buf *i_dma_buf;
>> +    size_t size;
>> +    unsigned long offset;
>> +    struct dma_buf *e_dma_buf;
>> +
>> +    struct dma_buf_attachment *attachment;
>> +    struct sg_table *sgt;
>> +
>> +    struct list_head attachments;
>> +    int map_count;
>> +
>> +    struct mutex lock;
>> +};
>> +
>> +static const struct regmap_config ti_pat_regmap_config = {
>> +    .reg_bits = 32,
>> +    .val_bits = 32,
>> +    .reg_stride = 4,
>> +};
>> +
>> +static int ti_pat_dma_buf_attach(struct dma_buf *dmabuf,
>> +                 struct dma_buf_attachment *attachment)
>> +{
>> +    struct ti_pat_dma_buf_attachment *a;
>> +    struct ti_pat_buffer *buffer = dmabuf->priv;
>> +
>> +    a = kzalloc(sizeof(*a), GFP_KERNEL);
>> +    if (!a)
>> +        return -ENOMEM;
>> +
>> +    a->dev = attachment->dev;
>> +    a->buffer = buffer;
>> +    INIT_LIST_HEAD(&a->list);
>> +
>> +    a->table = kzalloc(sizeof(*a->table), GFP_KERNEL);
>> +    if (!a->table) {
>> +        kfree(a);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    if (sg_alloc_table(a->table, 1, GFP_KERNEL)) {
>> +        kfree(a->table);
>> +        kfree(a);
>> +        return -ENOMEM;
>> +    }
>> +
>> +    sg_set_page(a->table->sgl, pfn_to_page(PFN_DOWN(buffer->offset)),
>> buffer->size, 0);
>> +
>> +    attachment->priv = a;
>> +
>> +    mutex_lock(&buffer->lock);
>> +    /* First time attachment we attach to parent */
>> +    if (list_empty(&buffer->attachments)) {
>> +        buffer->attachment = dma_buf_attach(buffer->i_dma_buf,
>> buffer->pat->dev);
>> +        if (IS_ERR(buffer->attachment)) {
>> +            dev_err(buffer->pat->dev, "Unable to attach to parent
>> DMA-BUF\n");
>> +            mutex_unlock(&buffer->lock);
>> +            kfree(a->table);
>> +            kfree(a);
>> +            return PTR_ERR(buffer->attachment);
>> +        }
>> +    }
>> +    list_add(&a->list, &buffer->attachments);
>> +    mutex_unlock(&buffer->lock);
>> +
>> +    return 0;
>> +}
>> +
>> +static void ti_pat_dma_buf_detatch(struct dma_buf *dmabuf,
>> +                   struct dma_buf_attachment *attachment)
> 
> Func name should be ti_pat_dma_buf_detach instead?
> 

Good catch, will fix.

> Other than that, I can't see anything obvious with my limited experience
> with dma_buf. Is there a simple way to test this driver btw?
> 

Simple way? No not really.. What I've been doing is allocating a
non-contiguous buffer (from system DMA-BUF heaps), writing some test
pattern to it, using this driver to convert the buffer, then sending the
new handle to our DSS (display subsystem which cannot handle
non-contiguous buffers). If all is working the test pattern is displayed
correctly.

Thanks,
Andrew

> -Tero
> 
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