Date:   Mon, 10 Jan 2022 17:15:26 -0500
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     Stafford Horne <shorne@...il.com>
Cc:     linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, ulf.hansson@...aro.org,
        linux-mmc@...r.kernel.org, kgugala@...micro.com,
        mholenko@...micro.com, krakoczy@...micro.com,
        mdudek@...ernships.antmicro.com, paulus@...abs.org, joel@....id.au,
        geert@...ux-m68k.org, david.abdurachmanov@...ive.com,
        florent@...oy-digital.fr, rdunlap@...radead.org,
        andy.shevchenko@...il.com, hdanton@...a.com
Subject: Re: [PATCH v11 3/3] mmc: Add driver for LiteX's LiteSDCard interface

On Tue, Jan 11, 2022 at 07:07:47AM +0900, Stafford Horne wrote:
> On Sun, Jan 09, 2022 at 06:20:03PM -0500, Gabriel Somlo wrote:
> > LiteX (https://github.com/enjoy-digital/litex) is a SoC framework
> > that targets FPGAs. LiteSDCard is a small footprint, configurable
> > SDCard core commonly used in LiteX designs.
> > 
> > The driver was first written in May 2020 and has been maintained
> > cooperatively by the LiteX community. Thanks to all contributors!
> > 
> > Co-developed-by: Kamil Rakoczy <krakoczy@...micro.com>
> > Signed-off-by: Kamil Rakoczy <krakoczy@...micro.com>
> > Co-developed-by: Maciej Dudek <mdudek@...ernships.antmicro.com>
> > Signed-off-by: Maciej Dudek <mdudek@...ernships.antmicro.com>
> > Co-developed-by: Paul Mackerras <paulus@...abs.org>
> > Signed-off-by: Paul Mackerras <paulus@...abs.org>
> > Signed-off-by: Gabriel Somlo <gsomlo@...il.com>
> > Reviewed-by: Joel Stanley <joel@....id.au>
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
> > ---
> > 
> > New in v11:
> >   - picked up r/b from Andy
> > drivers/mmc/host/litex_mmc.c:
> >   - defensive coding of litex_mmc_interrupt() return logic
> >   - remove `dev` member of `struct litex_mmc_host`, only used during probe
> > 
> > >New in v10:
> > >drivers/mmc/host/litex_mmc.c:
> > >  - group `linux/mmc/*` includes by themselves
> > >  - clean-up of `return` style (multiple locations throughout source)
> > >  - create `mmc_free_host()` wrapper for use with 
> > >    `devm_add_action_or_reset()`
> > >  - use GFP_KERNEL with `dmam_alloc_coherent()`
> > >
> > >>New in v9:
> > >>drivers/mmc/host/Kconfig:
> > >>  - fix OF dependency
> > >>drivers/mmc/host/litex_mmc.c:
> > >>  - remove `linux/of.h` include, no longer needed since dropping
> > >>    `of_match_ptr()`
> > >>  - add `linux/mod_devicetable.h` include
> > >>  - use devm_action_or_reset() to devm-ify mmc_alloc_host(), and obviate
> > >>    the need to call mmc_free_host() explicitly during either probe()
> > >>    error path or during remove()
> > >>
> > >>>New in v8:
> > >>>  - remove `Cc:` lines from commit blurb
> > >>>drivers/mmc/host/litex_mmc.c:
> > >>>  - fix file header comment (for real, this time)
> > >>>  - add explicit `bits.h` include
> > >>>  - remove `of_match_ptr()` wrapper from around .of_match_table argument
> > >>>  - fix devm ordering issues: use `devm_request_irq()`, which precludes
> > >>>    the need to call `free_irq()` on `probe()` error path or from `remove()`
> > >>>
> > >>>>New in v7:
> > >>>>drivers/mmc/host/Kconfig:
> > >>>>  - added module name in LiteSDCard Kconfig entry
> > >>>>drivers/mmc/host/litex_mmc.c:
> > >>>>  - fixed comment formatting, ordering, and capitalization throughout
> > >>>>    the entire file
> > >>>>  - sorted header #include statements
> > >>>>  - removed redundant parantheses in readx_poll_timeout() condition
> > >>>>  - explicit handling of readx_poll_timeout() timeout scenarios
> > >>>>  - dev_err() used in litex_mmc_sdcard_wait_done()
> > >>>>  - use memcpy_fromio() to grab command response
> > >>>>  - no need to apply 0xffff mask to a 32-bit value right-shifted by 16
> > >>>>    (host->resp[3])
> > >>>>  - use clamp() instead of min(max(...)...)
> > >>>>  - reworked platform_get_irq_optional() error handling logic
> > >>>>  - no need to explicitly zero host->irq, kzalloc() does that already
> > >>>>  - added missing free_irq() in litex_mmc_probe() error path
> > >>>>  - reordered calls inside litex_mmc_remove() (calling mmc_free_host()
> > >>>>    before free_irq()
> > >>>>
> > >>>>>New in v6:
> > >>>>>  - fix handling of deferred probe vs. platform_get_irq_optional()
> > >>>>>  - don't #ifdef dma_set_mask_and_coherent(), since it automatically
> > >>>>>    does the right thing on both 32- and 64-bit DMA capable arches
> > >>>>>  - remove MMC_CAP2_FULL_PWR_CYCLE, add MMC_CAP2_NO_MMC to list of
> > >>>>>    hardcoded capabilities during litex_mmc_probe()
> > >>>>>  - hardcode mmc->ocr_avail to the full 2.7-3.6V range allowed by the
> > >>>>>    SDCard spec (the LiteSDCard device doesn't accept software
> > >>>>>    configuration)
> > >>>>>
> > >>>>>>New in v5:
> > >>>>>>  - shorter #define constant names (cosmetic, make them less unwieldy)
> > >>>>>>  - picked up reviewed-by Joel
> > >>>>>>
> > >>>>>>>New in v4:
> > >>>>>>>  - struct litex_mmc_host fields re-ordered so that `pahole` reports
> > >>>>>>>    no holes on either 32- or 64-bit builds
> > >>>>>>>  - litex_mmc_set_bus_width() now encapsulates check for
> > >>>>>>>    host->is_bus_width_set
> > >>>>>>>  - litex_mmc_request() - factor out dma data setup into separate
> > >>>>>>>    helper function: litex_mmc_do_dma()
> > >>>>>>>
> > >>>>>>>> New in v3:
> > >>>>>>>>   - fixed function signature (no line split), and naming (litex_mmc_*)
> > >>>>>>>>   - more informative MODULE_AUTHOR() entries
> > >>>>>>>>     - also added matching "Copyright" entries in file header
> > >>>>>>>>   - fixed description and dependencies in Kconfig
> > >>>>>>>>   - removed magic constants
> > >>>>>>>>   - removed litex_map_status(), have sdcard_wait_done() return *real*
> > >>>>>>>>     error codes directly instead.
> > >>>>>>>>   - streamlined litex_mmc_reponse_len()
> > >>>>>>>>   - call litex_mmc_set_bus_width() only once, and ensure it returns
> > >>>>>>>>     correct error code(s)
> > >>>>>>>>   - use readx_poll_timeout() -- more concise -- instead of
> > >>>>>>>>     read_poll_timeout()
> > >>>>>>>>   - use dev_err() in litex_mmc_send_cmd() (instead of pr_err())
> > >>>>>>>>   - litex_mmc_setclk() will update host->clock before returning
> > >>>>>>>>   - separate irq initialization into its own function,
> > >>>>>>>>     litex_mmc_irq_init()
> > >>>>>>>>   - document rationale for f_min, f_max
> > >>>>>>>>   - use dmam_alloc_coherent(), which simplifies cleanup significantly
> > >>>>>>>>   - bump dma_set_mask_and_coherent() to 64-bits on suitable
> > >>>>>>>>     architectures
> > >>>>>>>>   - clock source picked up from dedicated DT clock reference property
> > >>>>>>>>   - remove gpio card-detect logic (needs testing and a dt binding
> > >>>>>>>>     example before being eligible for upstream inclusion)
> > >>>>>>>>   - large `if (data) { ... }` block in litex_mmc_request() left as-is,
> > >>>>>>>>     there are too many variables shared with the rest of the parent
> > >>>>>>>>     function body to easily separate (e.g., `len`, `transfer`, `direct`).
> > >>>>>>>>     If this is indeed a blocker, I can take another shot at refactoring
> > >>>>>>>>     it in a future revision!
> > 
> >  drivers/mmc/host/Kconfig     |   9 +
> >  drivers/mmc/host/Makefile    |   1 +
> >  drivers/mmc/host/litex_mmc.c | 657 +++++++++++++++++++++++++++++++++++
> >  3 files changed, 667 insertions(+)
> >  create mode 100644 drivers/mmc/host/litex_mmc.c
> > 
> > diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
> > index 5af8494c31b5..8f661f52b502 100644
> > --- a/drivers/mmc/host/Kconfig
> > +++ b/drivers/mmc/host/Kconfig
> > @@ -1093,3 +1093,12 @@ config MMC_OWL
> >  
> >  config MMC_SDHCI_EXTERNAL_DMA
> >  	bool
> > +
> > +config MMC_LITEX
> > +	tristate "LiteX MMC Host Controller support"
> > +	depends on ((PPC_MICROWATT || LITEX) && OF) || COMPILE_TEST
> > +	help
> > +	  This selects support for the MMC Host Controller found in LiteX SoCs.
> 
> See comment below.
> 
> > +	  To compile this driver as a module, choose M here: the
> > +	  module will be called litex_mmc.
> 
> Can we add this here too?
> 
> 	If unsure, say N.

OK, lined up for v12.

> > diff --git a/drivers/mmc/host/Makefile b/drivers/mmc/host/Makefile
> > index ea36d379bd3c..4e4ceb32c4b4 100644
> > --- a/drivers/mmc/host/Makefile
> > +++ b/drivers/mmc/host/Makefile
> > @@ -101,6 +101,7 @@ obj-$(CONFIG_MMC_CQHCI)			+= cqhci.o
> >  cqhci-y					+= cqhci-core.o
> >  cqhci-$(CONFIG_MMC_CRYPTO)		+= cqhci-crypto.o
> >  obj-$(CONFIG_MMC_HSQ)			+= mmc_hsq.o
> > +obj-$(CONFIG_MMC_LITEX)			+= litex_mmc.o
> >  
> >  ifeq ($(CONFIG_CB710_DEBUG),y)
> >  	CFLAGS-cb710-mmc	+= -DDEBUG
> > diff --git a/drivers/mmc/host/litex_mmc.c b/drivers/mmc/host/litex_mmc.c
> > new file mode 100644
> > index 000000000000..cc2848030e6b
> > --- /dev/null
> > +++ b/drivers/mmc/host/litex_mmc.c
> > @@ -0,0 +1,657 @@
> ...
> > +
> > +	/* Initialize clock source */
> > +	clk = devm_clk_get(dev, NULL);
> > +	if (IS_ERR(clk))
> > +		return dev_err_probe(dev, PTR_ERR(clk), "can't get clock\n");
> > +	host->ref_clk = clk_get_rate(clk);
> 
> Note, we used to have:
> 
> 	cpu = of_get_next_cpu_node(NULL);
> 	ret = of_property_read_u32(cpu, "clock-frequency", &host->freq);
> 	of_node_put(cpu);
> 	if (ret) {
> 		dev_err(&pdev->dev, "No \"clock-frequency\" property in DT\n");
> 		goto err_free_host;
> 	}
> 
> As we agree, this worked but was hacky.  The new use of devm_clk_get above uses
> the COMMON_CLK framework.  Which is great but OpenRISC doesn't yet support
> COMMON_CLK, so this driver no longer works on OpenRISC.
> 
> I think the ideal thing is to not change the driver code and I will just add
> support for COMMON_CLK on openrisc (already done and tested).  But as we
> discussed off e-mail I think we should change the config constraints to.
> 
>     depends on ((PPC_MICROWATT || LITEX) && OF && HAVE_CLK) || COMPILE_TEST

OK, also lined up for v12.

I'll probably send out v12 in a few hours -- thanks for the
suggestions and testing!

Best,
--Gabriel

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