Date:   Fri, 20 Oct 2017 17:25:19 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, rob.walker@....com,
        mike.leach@...aro.org, coresight@...ts.linaro.org,
        mathieu.poirier@...aro.org
Subject: Re: [PATCH 05/17] coresight: Add support for TMC ETR SG unit

Hi Suzuki,

On 19/10/17 18:15, Suzuki K Poulose wrote:
> This patch adds support for setting up an SG table used by the
> TMC ETR inbuilt SG unit. The TMC ETR uses 4K page sized tables
> to hold pointers to the 4K data pages with the last entry in a
> table pointing to the next table with the entries, by kind of
> chaining. The 2 LSBs determine the type of the table entry, to
> one of :
> 
>   Normal - Points to a 4KB data page.
>   Last   - Points to a 4KB data page, but is the last entry in the
>            page table.
>   Link   - Points to another 4KB table page with pointers to data.
> 
> The code takes care of handling the system page size which could
> be different than 4K. So we could end up putting multiple ETR
> SG tables in a single system page, vice versa for the data pages.
> 
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>   drivers/hwtracing/coresight/coresight-tmc-etr.c | 256 ++++++++++++++++++++++++
>   1 file changed, 256 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 4b9e2b276122..4424eb67a54c 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -21,6 +21,89 @@
>   #include "coresight-tmc.h"
>   
>   /*
> + * The TMC ETR SG has a page size of 4K. The SG table contains pointers
> + * to 4KB buffers. However, the OS may be use PAGE_SIZE different from

nit:
"the OS may use a PAGE_SIZE different from".

> + * 4K (i.e, 16KB or 64KB). This implies that a single OS page could
> + * contain more than one SG buffer and tables.
> + *
> + * A table entry has the following format:
> + *
> + * ---Bit31------------Bit4-------Bit1-----Bit0--
> + * |     Address[39:12]    | SBZ |  Entry Type  |
> + * ----------------------------------------------
> + *
> + * Address: Bits [39:12] of a physical page address. Bits [11:0] are
> + *	    always zero.
> + *
> + * Entry type:
> + *	b00 - Reserved.
> + *	b01 - Last entry in the tables, points to 4K page buffer.
> + *	b10 - Normal entry, points to 4K page buffer.
> + *	b11 - Link. The address points to the base of next table.
> + */
> +
> +typedef u32 sgte_t;
> +
> +#define ETR_SG_PAGE_SHIFT		12
> +#define ETR_SG_PAGE_SIZE		(1UL << ETR_SG_PAGE_SHIFT)
> +#define ETR_SG_PAGES_PER_SYSPAGE	(1UL << \
> +					 (PAGE_SHIFT - ETR_SG_PAGE_SHIFT))

I think this would be slightly easier to understand if defined as:
"(PAGE_SIZE / ETR_SG_PAGE_SIZE)".

> +#define ETR_SG_PTRS_PER_PAGE		(ETR_SG_PAGE_SIZE / sizeof(sgte_t))
> +#define ETR_SG_PTRS_PER_SYSPAGE		(PAGE_SIZE / sizeof(sgte_t))
> +
> +#define ETR_SG_ET_MASK			0x3
> +#define ETR_SG_ET_LAST			0x1
> +#define ETR_SG_ET_NORMAL		0x2
> +#define ETR_SG_ET_LINK			0x3
> +
> +#define ETR_SG_ADDR_SHIFT		4
> +
> +#define ETR_SG_ENTRY(addr, type) \
> +	(sgte_t)((((addr) >> ETR_SG_PAGE_SHIFT) << ETR_SG_ADDR_SHIFT) | \
> +		 (type & ETR_SG_ET_MASK))
> +
> +#define ETR_SG_ADDR(entry) \
> +	(((dma_addr_t)(entry) >> ETR_SG_ADDR_SHIFT) << ETR_SG_PAGE_SHIFT)
> +#define ETR_SG_ET(entry)		((entry) & ETR_SG_ET_MASK)
> +
> +/*
> + * struct etr_sg_table : ETR SG Table
> + * @sg_table:		Generic SG Table holding the data/table pages.
> + * @hwaddr:		hwaddress used by the TMC, which is the base
> + *			address of the table.
> + */
> +struct etr_sg_table {
> +	struct tmc_sg_table	*sg_table;
> +	dma_addr_t		hwaddr;
> +};
> +
> +/*
> + * tmc_etr_sg_table_entries: Total number of table entries required to map
> + * @nr_pages system pages.
> + *
> + * We need to map @nr_pages * ETR_SG_PAGES_PER_SYSPAGE data pages.
> + * Each TMC page can map (ETR_SG_PTRS_PER_PAGE - 1) buffer pointers,
> + * with the last entry pointing to the page containing the table
> + * entries. If we spill over to a new page for mapping 1 entry,
> + * we could as well replace the link entry of the previous page
> + * with the last entry.
> + */
> +static inline unsigned long __attribute_const__
> +tmc_etr_sg_table_entries(int nr_pages)
> +{
> +	unsigned long nr_sgpages = nr_pages * ETR_SG_PAGES_PER_SYSPAGE;
> +	unsigned long nr_sglinks = nr_sgpages / (ETR_SG_PTRS_PER_PAGE - 1);
> +	/*
> +	 * If we spill over to a new page for 1 entry, we could as well
> +	 * make it the LAST entry in the previous page, skipping the Link
> +	 * address.
> +	 */
> +	if (nr_sglinks && (nr_sgpages % (ETR_SG_PTRS_PER_PAGE - 1) < 2))
> +		nr_sglinks--;
> +	return nr_sgpages + nr_sglinks;
> +}
> +
> +/*
>    * tmc_pages_get_offset:  Go through all the pages in the tmc_pages
>    * and map @phys_addr to an offset within the buffer.
>    */
> @@ -307,6 +390,179 @@ ssize_t tmc_sg_table_get_data(struct tmc_sg_table *sg_table,
>   	return len;
>   }
>   
> +#ifdef ETR_SG_DEBUG
> +/* Map a dma address to virtual address */
> +static unsigned long
> +tmc_sg_daddr_to_vaddr(struct tmc_sg_table *sg_table,
> +			dma_addr_t addr, bool table)
> +{
> +	long offset;
> +	unsigned long base;
> +	struct tmc_pages *tmc_pages;
> +
> +	if (table) {
> +		tmc_pages = &sg_table->table_pages;
> +		base = (unsigned long)sg_table->table_vaddr;
> +	} else {
> +		tmc_pages = &sg_table->data_pages;
> +		base = (unsigned long)sg_table->data_vaddr;
> +	}
> +
> +	offset = tmc_pages_get_offset(tmc_pages, addr);
> +	if (offset < 0)
> +		return 0;
> +	return base + offset;
> +}
> +
> +/* Dump the given sg_table */
> +static void tmc_etr_sg_table_dump(struct etr_sg_table *etr_table)
> +{
> +	sgte_t *ptr;
> +	int i = 0;
> +	dma_addr_t addr;
> +	struct tmc_sg_table *sg_table = etr_table->sg_table;
> +
> +	ptr = (sgte_t *)tmc_sg_daddr_to_vaddr(sg_table,
> +					      etr_table->hwaddr, true);
> +	while (ptr) {
> +		addr = ETR_SG_ADDR(*ptr);
> +		switch (ETR_SG_ET(*ptr)) {
> +		case ETR_SG_ET_NORMAL:
> +			pr_debug("%05d: %p\t:[N] 0x%llx\n", i, ptr, addr);
> +			ptr++;
> +			break;
> +		case ETR_SG_ET_LINK:
> +			pr_debug("%05d: *** %p\t:{L} 0x%llx ***\n",
> +				 i, ptr, addr);
> +			ptr = (sgte_t *)tmc_sg_daddr_to_vaddr(sg_table,
> +							      addr, true);
> +			break;
> +		case ETR_SG_ET_LAST:
> +			pr_debug("%05d: ### %p\t:[L] 0x%llx ###\n",
> +				 i, ptr, addr);
> +			return;

I get this is debug code, but it seems like if ETR_SG_ET(*ptr) is 0 we 
get stuck in an infinite loop. I guess it is something that supposedly 
doesn't happen, still I'd prefer having a default case saying the table 
might be corrupted and either incrementing ptr to try and get more info 
or breaking out of the loop.

> +		}
> +		i++;
> +	}
> +	pr_debug("******* End of Table *****\n");
> +}
> +#endif
> +
> +/*
> + * Populate the SG Table page table entries from table/data
> + * pages allocated. Each Data page has ETR_SG_PAGES_PER_SYSPAGE SG pages.
> + * So does a Table page. So we keep track of indices of the tables
> + * in each system page and move the pointers accordingly.
> + */
> +#define INC_IDX_ROUND(idx, size) (idx = (idx + 1) % size)

Needs more parenthesis around idx and size.

> +static void tmc_etr_sg_table_populate(struct etr_sg_table *etr_table)
> +{
> +	dma_addr_t paddr;
> +	int i, type, nr_entries;
> +	int tpidx = 0; /* index to the current system table_page */
> +	int sgtidx = 0;	/* index to the sg_table within the current syspage */
> +	int sgtoffset = 0; /* offset to the next entry within the sg_table */

That's misleading, this seems to be the index of an entry within an 
ETR_SG_PAGE rather than an offset in bytes.

Maybe ptridx or entryidx would be a better name.

> +	int dpidx = 0; /* index to the current system data_page */
> +	int spidx = 0; /* index to the SG page within the current data page */
> +	sgte_t *ptr; /* pointer to the table entry to fill */
> +	struct tmc_sg_table *sg_table = etr_table->sg_table;
> +	dma_addr_t *table_daddrs = sg_table->table_pages.daddrs;
> +	dma_addr_t *data_daddrs = sg_table->data_pages.daddrs;
> +
> +	nr_entries = tmc_etr_sg_table_entries(sg_table->data_pages.nr_pages);
> +	/*
> +	 * Use the contiguous virtual address of the table to update entries.
> +	 */
> +	ptr = sg_table->table_vaddr;
> +	/*
> +	 * Fill all the entries, except the last entry to avoid special
> +	 * checks within the loop.
> +	 */
> +	for (i = 0; i < nr_entries - 1; i++) {
> +		if (sgtoffset == ETR_SG_PTRS_PER_PAGE - 1) {
> +			/*
> +			 * Last entry in a sg_table page is a link address to
> +			 * the next table page. If this sg_table is the last
> +			 * one in the system page, it links to the first
> +			 * sg_table in the next system page. Otherwise, it
> +			 * links to the next sg_table page within the system
> +			 * page.
> +			 */
> +			if (sgtidx == ETR_SG_PAGES_PER_SYSPAGE - 1) {
> +				paddr = table_daddrs[tpidx + 1];
> +			} else {
> +				paddr = table_daddrs[tpidx] +
> +					(ETR_SG_PAGE_SIZE * (sgtidx + 1));
> +			}
> +			type = ETR_SG_ET_LINK;
> +		} else {
> +			/*
> +			 * Update the idices to the data_pages to point to the

nit: indices

Cheers,

-- 
Julien Thierry

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