Re: [PATCH 3/4] drivers: ddr: imx8m: ddr_init.c: support ECC scrubbing

[David Jander <david@protonic.nl>]

Hi Ahmad,

On Wed, 4 Mar 2026 12:43:55 +0100
Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:

> Hi,
> 
> On 3/4/26 12:23 PM, Steffen Trumtrar wrote:
> > From: David Jander <david@protonic.nl>
> > 
> > This code comes from u-boot [1] and was introducesd in commit [2].
> > 
> > A fix from the patch [3] is also included, which doesn't seem to be
> > added to u-boot, yet.
> > 
> > [1] https://github.com/u-boot/u-boot/
> > [2] commit f3acb02386f4 ("drivers: ddr: imx8mp: Add inline ECC feature support")
> > [3] https://patchwork.ozlabs.org/project/uboot/patch/20230123091702.7472-32-peng.fan@oss.nxp.com/
> > 
> > Signed-off-by: David Jander <david@protonic.nl>
> > Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
> > ---
> >  arch/arm/mach-imx/Kconfig        |  8 +++++
> >  drivers/ddr/imx/imx8m_ddr_init.c | 73 ++++++++++++++++++++++++++++++++++++++++
> >  include/soc/imx8m/ddr.h          | 11 ++++++
> >  3 files changed, 92 insertions(+)
> > 
> > diff --git a/arch/arm/mach-imx/Kconfig b/arch/arm/mach-imx/Kconfig
> > index d244c57580..75b04cf70f 100644
> > --- a/arch/arm/mach-imx/Kconfig
> > +++ b/arch/arm/mach-imx/Kconfig
> > @@ -1026,6 +1026,14 @@ config HABV3_IMG_CRT_DER
> >  
> >  endif
> >  
> > +config IMX8MP_DRAM_ECC
> > +	bool "Enable LPDDR4 ECC feature on i.MX8MP boards"
> > +	depends on ARCH_IMX8MP
> > +	help
> > +	  The i.MX8MP SoC supports ECC on the LPDDR4 memory. Select Y to enable
> > +	  this feature. The total amount of memory available will be reduced by
> > +	  1/8th.  
> 
> A generic option is too confusing when it's only affecting a single board.

Why should it affect only a single board? This is a general feature of this
SoC and it can be enabled for any other board that uses this SoC with LPDDR4
chips.

Even more so, I suspect this feature is present on some other SoCs as well
which use the same Synopsys DesignWare IP with this feature enabled. In that
case you'd probably want to make a more generic dram driver though. I suspect
chips like the Rockchip RK3588 or RK3576 might support this also, but I
haven't tried, and since those chips have binary dram init blobs this is
probably not easy to figure out.

Best regards,

> Alternative suggestion:
> 
>   - make IMX8MP_DRAM_ECC a hidden symbol
>   - select it from the protonic board
>   - Turn the RAM timings of the protonic board into a header and
>     replace #ifdef CONFIG_IMX8MP_DRAM_ECC with #ifdef USE_ECC
>   - Add two source code files, that include the new header once with
>     USE_ECC supported and once without
>   - Add two entry points which only differ in what RAM timings are used
> 
> Also worth considering: adding the size of the region to be scrubbed or
> the function doing the scrubbing into dram_timing_info.
> 
> Thoughts?
> 
> Cheers,
> Ahmad
> 
> > +
> >  endmenu
> >  
> >  endif
> > diff --git a/drivers/ddr/imx/imx8m_ddr_init.c b/drivers/ddr/imx/imx8m_ddr_init.c
> > index c16e04d274..6398a2b971 100644
> > --- a/drivers/ddr/imx/imx8m_ddr_init.c
> > +++ b/drivers/ddr/imx/imx8m_ddr_init.c
> > @@ -45,6 +45,74 @@ static void ddr_cfg_umctl2(struct dram_controller *dram, struct dram_cfg_param *
> >  	}
> >  }
> >  
> > +#ifdef CONFIG_IMX8MP_DRAM_ECC
> > +void ddrc_inline_ecc_scrub(unsigned int start_address,
> > +			   unsigned int range_address)
> > +{
> > +	unsigned int tmp;
> > +
> > +	pr_debug("ECC scrub %08x-%08x\n", start_address, range_address);
> > +	/* Step1: Enable quasi-dynamic programming */
> > +	reg32_write(DDRC_SWCTL(0), 0x00000000);
> > +	/* Step2: Set ECCCFG1.ecc_parity_region_lock to 1 */
> > +	reg32setbit(DDRC_ECCCFG1(0), 0x4);
> > +	/* Step3: Block the AXI ports from taking the transaction */
> > +	reg32_write(DDRC_PCTRL_0(0), 0x0);
> > +	/* Step4: Set scrub start address */
> > +	reg32_write(DDRC_SBRSTART0(0), start_address);
> > +	/* Step5: Set scrub range address */
> > +	reg32_write(DDRC_SBRRANGE0(0), range_address);
> > +	/* Step6: Set scrub_mode to write */
> > +	reg32_write(DDRC_SBRCTL(0), 0x00000014);
> > +	/* Step7: Set the desired pattern through SBRWDATA0 registers */
> > +	reg32_write(DDRC_SBRWDATA0(0), 0x55aa55aa);
> > +	/* Step8: Enable the SBR by programming SBRCTL.scrub_en=1 */
> > +	reg32setbit(DDRC_SBRCTL(0), 0x0);
> > +	/* Step9: Poll SBRSTAT.scrub_done=1 */
> > +	tmp = reg32_read(DDRC_SBRSTAT(0));
> > +	while (tmp != 0x00000002)
> > +		tmp = reg32_read(DDRC_SBRSTAT(0)) & 0x2;
> > +	/* Step10: Poll SBRSTAT.scrub_busy=0 */
> > +	tmp = reg32_read(DDRC_SBRSTAT(0));
> > +	while (tmp != 0x0)
> > +		tmp = reg32_read(DDRC_SBRSTAT(0)) & 0x1;
> > +	/* Step11: Disable SBR by programming SBRCTL.scrub_en=0 */
> > +	clrbits_le32(DDRC_SBRCTL(0), 0x1);
> > +	/* Step12: Prepare for normal scrub operation(Read) and set scrub_interval*/
> > +	reg32_write(DDRC_SBRCTL(0), 0xff20);
> > +	/* Step13: Enable the SBR by programming SBRCTL.scrub_en=1 */
> > +	reg32_write(DDRC_SBRCTL(0), 0xff21);
> > +	/* Step14: Enable AXI ports by programming */
> > +	reg32_write(DDRC_PCTRL_0(0), 0x1);
> > +	/* Step15: Disable quasi-dynamic programming */
> > +	reg32_write(DDRC_SWCTL(0), 0x00000001);
> > +}
> > +
> > +void ddrc_inline_ecc_scrub_end(unsigned int start_address,
> > +			       unsigned int range_address)
> > +{
> > +	pr_debug("ECC  end %08x-%08x\n", start_address, range_address);
> > +	/* Step1: Enable quasi-dynamic programming */
> > +	reg32_write(DDRC_SWCTL(0), 0x00000000);
> > +	/* Step2: Block the AXI ports from taking the transaction */
> > +	reg32_write(DDRC_PCTRL_0(0), 0x0);
> > +	/* Step3: Set scrub start address */
> > +	reg32_write(DDRC_SBRSTART0(0), start_address);
> > +	/* Step4: Set scrub range address */
> > +	reg32_write(DDRC_SBRRANGE0(0), range_address);
> > +	/* Step5: Disable SBR by programming SBRCTL.scrub_en=0 */
> > +	clrbits_le32(DDRC_SBRCTL(0), 0x1);
> > +	/* Step6: Prepare for normal scrub operation(Read) and set scrub_interval */
> > +	reg32_write(DDRC_SBRCTL(0), 0x100);
> > +	/* Step7: Enable the SBR by programming SBRCTL.scrub_en=1 */
> > +	reg32_write(DDRC_SBRCTL(0), 0x101);
> > +	/* Step8: Enable AXI ports by programming */
> > +	reg32_write(DDRC_PCTRL_0(0), 0x1);
> > +	/* Step9: Disable quasi-dynamic programming */
> > +	reg32_write(DDRC_SWCTL(0), 0x00000001);
> > +}
> > +#endif
> > +
> >  static unsigned int g_cdd_rr_max[4];
> >  static unsigned int g_cdd_rw_max[4];
> >  static unsigned int g_cdd_wr_max[4];
> > @@ -642,6 +710,11 @@ int imx8m_ddr_init(struct dram_controller *dram, struct dram_timing_info *dram_t
> >  	reg32_write(DDRC_PCTRL_0(0), 0x00000001);
> >  	pr_debug("ddrmix config done\n");
> >  
> > +#ifdef CONFIG_IMX8MP_DRAM_ECC
> > +	if (dram->ddrc_type == DDRC_TYPE_MP)
> > +		board_dram_ecc_scrub();
> > +#endif
> > +
> >  	/* save the dram timing config into memory */
> >  	dram_config_save(dram, dram_timing, IMX8M_SAVED_DRAM_TIMING_BASE);
> >  
> > diff --git a/include/soc/imx8m/ddr.h b/include/soc/imx8m/ddr.h
> > index 5df07772b3..08ebf61da0 100644
> > --- a/include/soc/imx8m/ddr.h
> > +++ b/include/soc/imx8m/ddr.h
> > @@ -186,6 +186,8 @@
> >  #define DDRC_SBRWDATA0(X)        (DDRC_IPS_BASE_ADDR(X) + 0xf2c)
> >  #define DDRC_SBRWDATA1(X)        (DDRC_IPS_BASE_ADDR(X) + 0xf30)
> >  #define DDRC_PDCH(X)             (DDRC_IPS_BASE_ADDR(X) + 0xf34)
> > +#define DDRC_SBRSTART0(X)        (DDRC_IPS_BASE_ADDR(X) + 0xf38)
> > +#define DDRC_SBRRANGE0(X)        (DDRC_IPS_BASE_ADDR(X) + 0xf40)
> >  
> >  #define DDRC_FREQ1_DERATEEN(X)         (DDRC_IPS_BASE_ADDR(X) + 0x2020)
> >  #define DDRC_FREQ1_DERATEINT(X)        (DDRC_IPS_BASE_ADDR(X) + 0x2024)
> > @@ -380,4 +382,13 @@ static inline void imx8m_ddr_load_train_code(enum dram_type dram_type,
> >  	ddr_load_train_code(&imx8m_dram_controller, dram_type, fw_type);
> >  }
> >  
> > +#define DDRC_PHY_REG(x)	((x) * 4)
> > +
> > +void board_dram_ecc_scrub(void);
> > +
> > +void ddrc_inline_ecc_scrub(unsigned int start_address,
> > +			   unsigned int range_address);
> > +void ddrc_inline_ecc_scrub_end(unsigned int start_address,
> > +			       unsigned int range_address);
> > +
> >  #endif
> >   
> 



-- 
David Jander