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Date: Wed, 1 Nov 2017 10:11:48 +0000 From: Suzuki K Poulose <Suzuki.Poulose@....com> To: Julien Thierry <julien.thierry@....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 >> 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". > >> +#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)". > >> +/* 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. You're right, I have chosen sgtentry for now. Thanks for the detailed look, I will fix all of them. Cheers Suzuki
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