Date:   Mon, 10 Jan 2022 17:39:36 -0500
From:   "Gabriel L. Somlo" <gsomlo@gmail.com>
To:     Stafford Horne <shorne@gmail.com>
Cc:     linux-kernel@vger.kernel.org, robh+dt@kernel.org,
        devicetree@vger.kernel.org, ulf.hansson@linaro.org,
        linux-mmc@vger.kernel.org, kgugala@antmicro.com,
        mholenko@antmicro.com, krakoczy@antmicro.com,
        mdudek@internships.antmicro.com, paulus@ozlabs.org, joel@jms.id.au,
        geert@linux-m68k.org, david.abdurachmanov@sifive.com,
        florent@enjoy-digital.fr, rdunlap@infradead.org,
        andy.shevchenko@gmail.com, hdanton@sina.com
Subject: Re: [PATCH v11 3/3] mmc: Add driver for LiteX's LiteSDCard interface
Message-ID: <Ydy1qCc3CXOWKv/O@errol.ini.cmu.edu>
References: <20220109232003.2573924-1-gsomlo@gmail.com>
 <20220109232003.2573924-4-gsomlo@gmail.com>
 <YdywDhEbYyzm7Rri@antec>
MIME-Version: 1.0
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In-Reply-To: <YdywDhEbYyzm7Rri@antec>
Precedence: bulk

On Tue, Jan 11, 2022 at 07:15:42AM +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@antmicro.com>
> > Signed-off-by: Kamil Rakoczy <krakoczy@antmicro.com>
> > Co-developed-by: Maciej Dudek <mdudek@internships.antmicro.com>
> > Signed-off-by: Maciej Dudek <mdudek@internships.antmicro.com>
> > Co-developed-by: Paul Mackerras <paulus@ozlabs.org>
> > Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> > Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
> > Reviewed-by: Joel Stanley <joel@jms.id.au>
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> > ---
> > 
> ...
> > +static int litex_mmc_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct litex_mmc_host *host;
> > +	struct mmc_host *mmc;
> > +	struct clk *clk;
> > +	int ret;
> > +
> > +	/*
> > +	 * NOTE: defaults to max_[req,seg]_size=PAGE_SIZE, max_blk_size=512,
> > +	 * and max_blk_count accordingly set to 8;
> > +	 * If for some reason we need to modify max_blk_count, we must also
> > +	 * re-calculate `max_[req,seg]_size = max_blk_size * max_blk_count;`
> > +	 */
> > +	mmc = mmc_alloc_host(sizeof(struct litex_mmc_host), dev);
> > +	if (!mmc)
> > +		return -ENOMEM;
> > +
> > +	ret = devm_add_action_or_reset(dev, litex_mmc_free_host_wrapper, mmc);
> > +	if (ret)
> > +		return dev_err_probe(dev, ret,
> > +				     "Can't register mmc_free_host action\n");
> > +
> > +	host = mmc_priv(mmc);
> > +	host->mmc = mmc;
> > +
> > +	/* 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);
> > +	host->sd_clk = 0;
> > +
> > +	/*
> > +	 * LiteSDCard only supports 4-bit bus width; therefore, we MUST inject
> > +	 * a SET_BUS_WIDTH (acmd6) before the very first data transfer, earlier
> > +	 * than when the mmc subsystem would normally get around to it!
> > +	 */
> > +	host->is_bus_width_set = false;
> > +	host->app_cmd = false;
> > +
> > +	/* LiteSDCard can support 64-bit DMA addressing */
> > +	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64));
> > +	if (ret)
> > +		return ret;
> > +
> > +	host->buf_size = mmc->max_req_size * 2;
> > +	host->buffer = dmam_alloc_coherent(dev, host->buf_size,
> > +					   &host->dma, GFP_KERNEL);
> > +	if (host->buffer == NULL)
> > +		return -ENOMEM;
> > +
> > +	host->sdphy = devm_platform_ioremap_resource_byname(pdev, "phy");
> > +	if (IS_ERR(host->sdphy))
> > +		return PTR_ERR(host->sdphy);
> > +
> > +	host->sdcore = devm_platform_ioremap_resource_byname(pdev, "core");
> > +	if (IS_ERR(host->sdcore))
> > +		return PTR_ERR(host->sdcore);
> > +
> > +	host->sdreader = devm_platform_ioremap_resource_byname(pdev, "reader");
> > +	if (IS_ERR(host->sdreader))
> > +		return PTR_ERR(host->sdreader);
> > +
> > +	host->sdwriter = devm_platform_ioremap_resource_byname(pdev, "writer");
> > +	if (IS_ERR(host->sdwriter))
> > +		return PTR_ERR(host->sdwriter);
> > +
> > +	/* Ensure DMA bus masters are disabled */
> > +	litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> > +	litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> > +
> > +	init_completion(&host->cmd_done);
> > +	ret = litex_mmc_irq_init(pdev, host);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Allow full generic 2.7-3.6V range; no software tuning available */
> > +	mmc->ocr_avail = LITEX_MMC_OCR;
> > +
> > +	mmc->ops = &litex_mmc_ops;
> > +
> > +	/*
> > +	 * Set default sd_clk frequency range based on empirical observations
> > +	 * of LiteSDCard gateware behavior on typical SDCard media
> > +	 */
> > +	mmc->f_min = 12.5e6;
> > +	mmc->f_max = 50e6;
> > +
> > +	ret = mmc_of_parse(mmc);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Force 4-bit bus_width (only width supported by hardware) */
> > +	mmc->caps &= ~MMC_CAP_8_BIT_DATA;
> > +	mmc->caps |= MMC_CAP_4_BIT_DATA;
> > +
> > +	/* Set default capabilities */
> > +	mmc->caps |= MMC_CAP_WAIT_WHILE_BUSY |
> > +		     MMC_CAP_DRIVER_TYPE_D |
> > +		     MMC_CAP_CMD23;
> > +	mmc->caps2 |= MMC_CAP2_NO_WRITE_PROTECT |
> > +		      MMC_CAP2_NO_SDIO |
> > +		      MMC_CAP2_NO_MMC;
> > +
> > +	platform_set_drvdata(pdev, host);
> 
> One more thing here. Or somewhere, should we add:
> 
> 	dev_info(dev, "Litex MMC controller initialized");
> 
> I was having a hard time debugging probing of this and having no printk's made
> it a bit difficult.
> 
> Though I was able to get most of the debug statements I needed using:
> 
> 	"debug initcall_debug dyndbg=\"file drivers/* +p\" loglevel=8"
> 
> -Stafford
> 
> > +	return mmc_add_host(mmc);

I'd prefer to declare victory *after* calling mmc_add_host(), so if
there are no objections I'd prefer to do the following in v12:

        ... 
        platform_set_drvdata(pdev, host);
 
-       return mmc_add_host(mmc);
+       ret = mmc_add_host(mmc);
+       if (ret)
+               return dev_err_probe(dev, ret, "LiteX MMC probe failed!\n");
+
+       dev_info(dev, "LiteX MMC controller initialized.\n");
+
+       return 0;
 }

Thanks,
--Gabriel