linux-kernel - Re: [RFC PATCH 00/10] OMAP: GPMC: NAND: Introduce GPMC APIs for OMAP NAND

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Date:	Thu, 10 Jul 2014 23:52:12 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Roger Quadros <rogerq@...com>
Cc:	computersforpeace@...il.com, javier@...hile0.org, pekon@...com,
	ezequiel.garcia@...e-electrons.com, dwmw2@...radead.org,
	jg1.han@...sung.com, nsekhar@...com, linux-mtd@...ts.infradead.org,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 00/10] OMAP: GPMC: NAND: Introduce GPMC APIs for OMAP
 NAND

* Roger Quadros <rogerq@...com> [140709 05:39]:
> Hi,
> 
> The following hardware modules/registers are meant for NAND controller driver
> usage:
> - NAND I/O control (NAND address, data, command registers)
> - Prefetch/Write-post engine
> - ECC/BCH engine
> 
> However, these registers sit in the GPMC controller's register space and there
> need to be some sane way to access them from the OMAP NAND controller driver.
> 
> Till now the GPMC driver was populating a data structure (struct gpmc_nand_regs)
> with the register addresses and passing it to the OMAP NAND driver via platform
> data. This mechanism cannot be used for true Device tree support as custom
> platform data passing mechanism doesn't seem to work. Moreover, direct
> access to these registers must be limited to the GPMC driver. This calls for
> a few custom OMAP GPMC specific APIs that the OMAP NAND driver can use
> to access these GPMC space registers.
> 
> This series attempts to add the following new APIs and gets rid of
> 'struct gpmc_nand_regs' and 'gpmc_update_nand_regs()'.
> 
> -For NAND I/O control registers
> u32 omap_gpmc_read_reg(int cs, enum omap_gpmc_reg reg);
> void omap_gpmc_write_reg(int cs, enum omap_gpmc_reg reg, u32 val);
> 
> -For Prefetch engine
> int omap_gpmc_prefetch_start(int cs, int fifo_th, bool dma,
> 			     u32 count, int is_write);
> int omap_gpmc_prefetch_stop(int cs);
> u32 omap_gpmc_get_prefetch_count(void);
> u32 omap_gpmc_get_prefetch_fifo_count(void);
> 
> -For ECC/BCH engine
> void omap_gpmc_ecc_disable(void);
> void omap_gpmc_ecc_configure_enable(int cs, bool ecc16, u8 ecc_size0,
> 				    u8 ecc_size1, bool use_bch,
> 				    enum omap_gpmc_bch_type bch_type,
> 				    u8 bch_sectors, u8 bch_wrap_mode);
> void omap_gpmc_ecc_get_result(int length, u32 *result);
> void omap_gpmc_ecc_get_bch_result(int length, u8 sector, u32 *result);

These seem fine to me. At least I don't have any better ideas to
expose these GPMC registers to the NAND driver(s).
 
> These APIs don't implement any logic to serialize access to the
> NAND/Prefetch/ECC registers. It is upto the NAND controller driver
> to ensure that. As these modules can only handle one NAND controller context
> at a time, we set the nand_chip->hwcontrol to point to a single
> controller instance even if there are multiple NAND chips on different
> Chip select spaces. The NAND base driver then takes care of serializing
> access to the NAND controller (and ECC) through nandchip->hwcontrol->lock.
> 
> NOTE: Patches are still untested and only meant for review.

Regards,

Tony
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