Re: [PATCH v2 3/3] mmc: Add driver for LiteX's LiteSDCard interface

Gabriel L. Somlo
2021-12-06T18:40:23Z

Hi Geert,

Thanks for the feedback. I've lined up most of it for v3 (which I'll
send out shortly). A couple of replies inline, below:

On Mon, Dec 06, 2021 at 11:07:56AM +0100, Geert Uytterhoeven wrote:
> On Sat, Dec 4, 2021 at 9:41 PM Gabriel Somlo <gsomlo@gmail.com> 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>
>
> Thanks for your patch!
>
> > --- /dev/null
> > +++ b/drivers/mmc/host/litex_mmc.c
>
> > +struct litex_mmc_host {
> > + struct mmc_host *mmc;
> > + struct platform_device *dev;
> > +
> > + void __iomem *sdphy;
> > + void __iomem *sdcore;
> > + void __iomem *sdreader;
> > + void __iomem *sdwriter;
> > + void __iomem *sdirq;
> > +
> > + u32 resp[4];
> > + u16 rca;
> > +
> > + void *buffer;
> > + size_t buf_size;
> > + dma_addr_t dma;
> > +
> > + unsigned int freq;
> > + unsigned int clock;
> > + bool is_bus_width_set;
> > + bool app_cmd;
> > +
> > + int irq;
> > + struct completion cmd_done;
>
> You may want to reorder the members to avoid implicit gaps
> (i.e. structs first, followed by integral types in decreasing size).

OK.

> > +};
> > +
> > +static int
> > +sdcard_wait_done(void __iomem *reg)
> > +{
> > + u8 evt;
> > + int ret;
> > +
> > + ret = read_poll_timeout(litex_read8, evt, (evt & 0x1),
>
> Lots of magic numbers. Please use defines, like
>
> #define EVT_FOO BIT(0)

Done.

> > + SD_SLEEP_US, SD_TIMEOUT_US, false, reg);
> > + if (ret || (evt & 0x4))
> > + return SD_TIMEOUT;
> > + if (evt == 0x1)
> > + return SD_OK;
> > + if (evt & 0x2)
> > + return SD_WRITEERROR;
> > + if (evt & 0x8)
> > + return SD_CRCERROR;
> > + pr_err("%s: unknown error evt=%x\n", __func__, evt);
> > + return SD_ERR_OTHER;
> > +}
> > +
> > +static int
> > +send_cmd(struct litex_mmc_host *host,
> > + u8 cmd, u32 arg, u8 response_len, u8 transfer)
> > +{
> > + void __iomem *reg;
> > + u8 i;
>
> unsigned int

OK.

> > + int status;
> > +
> > + litex_write32(host->sdcore + LITEX_CORE_CMDARG, arg);
> > + litex_write32(host->sdcore + LITEX_CORE_CMDCMD,
> > + cmd << 8 | transfer << 5 | response_len);
> > + litex_write8(host->sdcore + LITEX_CORE_CMDSND, 1);
> > +
> > + /* Wait for an interrupt if we have an interrupt and either there is
> > + * data to be transferred, or if the card can report busy via DAT0.
> > + */
> > + if (host->irq > 0 &&
> > + (transfer != SDCARD_CTRL_DATA_TRANSFER_NONE ||
> > + response_len == SDCARD_CTRL_RESPONSE_SHORT_BUSY)) {
> > + reinit_completion(&host->cmd_done);
> > + litex_write32(host->sdirq + LITEX_IRQ_ENABLE,
> > + SDIRQ_CMD_DONE | SDIRQ_CARD_DETECT);
> > + wait_for_completion(&host->cmd_done);
> > + }
> > +
> > + status = sdcard_wait_done(host->sdcore + LITEX_CORE_CMDEVT);
> > +
> > + if (status != SD_OK) {
> > + pr_err("Command (cmd %d) failed, status %d\n", cmd, status);
> > + return status;
> > + }
> > +
> > + if (response_len != SDCARD_CTRL_RESPONSE_NONE) {
> > + reg = host->sdcore + LITEX_CORE_CMDRSP;
> > + for (i = 0; i < 4; i++) {
> > + host->resp[i] = litex_read32(reg);
> > + reg += sizeof(u32);
> > + }
> > + }
> > +
> > + if (!host->app_cmd && cmd == SD_SEND_RELATIVE_ADDR)
> > + host->rca = (host->resp[3] >> 16) & 0xffff;
> > +
> > + host->app_cmd = (cmd == MMC_APP_CMD);
> > +
> > + if (transfer == SDCARD_CTRL_DATA_TRANSFER_NONE)
> > + return status; /* SD_OK from prior sdcard_wait_done(cmd_evt) */
> > +
> > + status = sdcard_wait_done(host->sdcore + LITEX_CORE_DATAEVT);
> > + if (status != SD_OK) {
> > + pr_err("Data xfer (cmd %d) failed, status %d\n", cmd, status);
> > + return status;
> > + }
> > +
> > + /* wait for completion of (read or write) DMA transfer */
> > + reg = (transfer == SDCARD_CTRL_DATA_TRANSFER_READ) ?
> > + host->sdreader + LITEX_BLK2MEM_DONE :
> > + host->sdwriter + LITEX_MEM2BLK_DONE;
> > +
> > + status = read_poll_timeout(litex_read8, i, (i & 0x1),
> > + SD_SLEEP_US, SD_TIMEOUT_US, false, reg);
> > + if (status)
> > + pr_err("DMA timeout (cmd %d)\n", cmd);
> > +
> > + return status;
> > +}
> > +
> > +static inline int
>
> No need for inline, the compiler can decide.

OK.

> > +send_app_cmd(struct litex_mmc_host *host)
> > +{
> > + return send_cmd(host, MMC_APP_CMD, host->rca << 16,
> > + SDCARD_CTRL_RESPONSE_SHORT,
> > + SDCARD_CTRL_DATA_TRANSFER_NONE);
> > +}
> > +
> > +static inline int
>
> Likewise.
>
> > +send_app_set_bus_width_cmd(struct litex_mmc_host *host, u32 width)
> > +{
> > + return send_cmd(host, SD_APP_SET_BUS_WIDTH, width,
> > + SDCARD_CTRL_RESPONSE_SHORT,
> > + SDCARD_CTRL_DATA_TRANSFER_NONE);
> > +}
>
> > +static int
> > +litex_get_cd(struct mmc_host *mmc)
>
> litex_mmc_get_cd()? (i.e. "litex_mmc_"-prefix everywhere)

Done, throughout the entire file.

> > +{
> > + struct litex_mmc_host *host = mmc_priv(mmc);
> > + int ret;
> > +
> > + if (!mmc_card_is_removable(mmc))
> > + return 1;
> > +
> > + ret = mmc_gpio_get_cd(mmc);
> > + if (ret >= 0)
> > + /* GPIO based card-detect explicitly specified in DTS */
> > + ret = !!ret;
> > + else
> > + /* use gateware card-detect bit by default */
> > + ret = !litex_read8(host->sdphy + LITEX_PHY_CARDDETECT);
>
> Please use curly braces to delimit blocks larger than a single line.

OK.

> > +
> > + /* ensure bus width will be set (again) upon card (re)insertion */
> > + if (ret == 0)
> > + host->is_bus_width_set = false;
> > +
> > + return ret;
> > +}
>
> > +static u32
> > +litex_response_len(struct mmc_command *cmd)
> > +{
> > + if (cmd->flags & MMC_RSP_136) {
> > + return SDCARD_CTRL_RESPONSE_LONG;
> > + } else if (cmd->flags & MMC_RSP_PRESENT) {
>
> No need for else after return.
>
> > + if (cmd->flags & MMC_RSP_BUSY)
> > + return SDCARD_CTRL_RESPONSE_SHORT_BUSY;
> > + else
> > + return SDCARD_CTRL_RESPONSE_SHORT;
> > + }
> > + return SDCARD_CTRL_RESPONSE_NONE;
>
> Perhaps it's worthwhile to invert the logic of the last check, to
> reduce indentation?
>
> if (cmd->flags & MMC_RSP_136)
> return SDCARD_CTRL_RESPONSE_LONG;
>
> if (!(cmd->flags & MMC_RSP_PRESENT))
> return SDCARD_CTRL_RESPONSE_NONE;
>
> if (cmd->flags & MMC_RSP_BUSY)
> return SDCARD_CTRL_RESPONSE_SHORT_BUSY;
>
> return SDCARD_CTRL_RESPONSE_SHORT;

Thanks, that's a good idea, and I did it just like you suggested!

> > +}
>
> > +static void
> > +litex_request(struct mmc_host *mmc, struct mmc_request *mrq)
> > +{
> > + struct litex_mmc_host *host = mmc_priv(mmc);
> > + struct platform_device *pdev = to_platform_device(mmc->parent);
> > + struct device *dev = &pdev->dev;
> > + struct mmc_data *data = mrq->data;
> > + struct mmc_command *sbc = mrq->sbc;
> > + struct mmc_command *cmd = mrq->cmd;
> > + struct mmc_command *stop = mrq->stop;
> > + unsigned int retries = cmd->retries;
> > + int status;
> > + int sg_count;
> > + enum dma_data_direction dir = DMA_TO_DEVICE;
> > + bool direct = false;
> > + dma_addr_t dma;
> > + unsigned int len = 0;
>
> The above might look nicer when using "reverse Xmas tree" order
> of declarations.

I did that *partially* -- still wanted to preserve grouping of
variables that tend to be related, but I think I fixed the most
"egregious" instances of visual mis-alignment :)

> > +
> > + u32 response_len = litex_response_len(cmd);
> > + u32 transfer = SDCARD_CTRL_DATA_TRANSFER_NONE;
> > +
> > + /* First check that the card is still there */
> > + if (!litex_get_cd(mmc)) {
> > + cmd->error = -ENOMEDIUM;
> > + mmc_request_done(mmc, mrq);
> > + return;
> > + }
> > +
> > + /* Send set-block-count command if needed */
> > + if (sbc) {
> > + status = send_cmd(host, sbc->opcode, sbc->arg,
> > + litex_response_len(sbc),
> > + SDCARD_CTRL_DATA_TRANSFER_NONE);
> > + sbc->error = litex_map_status(status);
> > + if (status != SD_OK) {
> > + host->is_bus_width_set = false;
> > + mmc_request_done(mmc, mrq);
> > + return;
> > + }
> > + }
> > +
> > + if (data) {
> > + /* 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!
> > + */
> > + if (!host->is_bus_width_set) {
> > + ulong n = jiffies + 2 * HZ; // 500ms timeout
> > +
> > + while (litex_set_bus_width(host) != SD_OK) {
> > + if (time_after(jiffies, n)) {
> > + dev_warn(dev, "Can't set bus width!\n");
> > + cmd->error = -ETIMEDOUT;
> > + mmc_request_done(mmc, mrq);
> > + return;
> > + }
> > + }
> > + host->is_bus_width_set = true;
> > + }
> > +
> > + /* Try to DMA directly to/from the data buffer.
> > + * We can do that if the buffer can be mapped for DMA
> > + * in one contiguous chunk.
> > + */
> > + dma = host->dma;
> > + len = data->blksz * data->blocks;
> > + if (data->flags & MMC_DATA_READ)
> > + dir = DMA_FROM_DEVICE;
> > + sg_count = dma_map_sg(&host->dev->dev,
> > + data->sg, data->sg_len, dir);
> > + if (sg_count == 1) {
> > + dma = sg_dma_address(data->sg);
> > + len = sg_dma_len(data->sg);
> > + direct = true;
> > + } else if (len > host->buf_size)
> > + len = host->buf_size;
> > +
> > + if (data->flags & MMC_DATA_READ) {
> > + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> > + litex_write64(host->sdreader + LITEX_BLK2MEM_BASE, dma);
> > + litex_write32(host->sdreader + LITEX_BLK2MEM_LEN, len);
> > + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 1);
> > +
> > + transfer = SDCARD_CTRL_DATA_TRANSFER_READ;
> > + } else if (data->flags & MMC_DATA_WRITE) {
> > + if (!direct)
> > + sg_copy_to_buffer(data->sg, data->sg_len,
> > + host->buffer, len);
> > +
> > + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> > + litex_write64(host->sdwriter + LITEX_MEM2BLK_BASE, dma);
> > + litex_write32(host->sdwriter + LITEX_MEM2BLK_LEN, len);
> > + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 1);
> > +
> > + transfer = SDCARD_CTRL_DATA_TRANSFER_WRITE;
> > + } else {
> > + dev_warn(dev, "Data present w/o read or write flag.\n");
> > + /* Continue: set cmd status, mark req done */
> > + }
> > +
> > + litex_write16(host->sdcore + LITEX_CORE_BLKLEN, data->blksz);
> > + litex_write32(host->sdcore + LITEX_CORE_BLKCNT, data->blocks);
> > + }
> > +
> > + do {
> > + status = send_cmd(host, cmd->opcode, cmd->arg,
> > + response_len, transfer);
> > + } while (status != SD_OK && retries-- > 0);
> > +
> > + cmd->error = litex_map_status(status);
> > + if (status != SD_OK)
> > + /* card may be gone; don't assume bus width is still set */
> > + host->is_bus_width_set = false;
>
> Please add curly braces.

OK.

> > +
> > + if (response_len == SDCARD_CTRL_RESPONSE_SHORT) {
> > + /* pull short response fields from appropriate host registers */
> > + cmd->resp[0] = host->resp[3];
> > + cmd->resp[1] = host->resp[2] & 0xFF;
> > + } else if (response_len == SDCARD_CTRL_RESPONSE_LONG) {
> > + cmd->resp[0] = host->resp[0];
> > + cmd->resp[1] = host->resp[1];
> > + cmd->resp[2] = host->resp[2];
> > + cmd->resp[3] = host->resp[3];
> > + }
> > +
> > + /* Send stop-transmission command if required */
> > + if (stop && (cmd->error || !sbc)) {
> > + int stop_stat;
> > +
> > + stop_stat = send_cmd(host, stop->opcode, stop->arg,
> > + litex_response_len(stop),
> > + SDCARD_CTRL_DATA_TRANSFER_NONE);
> > + stop->error = litex_map_status(stop_stat);
> > + if (stop_stat != SD_OK)
> > + host->is_bus_width_set = false;
> > + }
> > +
> > + if (data)
> > + dma_unmap_sg(&host->dev->dev, data->sg, data->sg_len, dir);
> > +
> > + if (status == SD_OK && transfer != SDCARD_CTRL_DATA_TRANSFER_NONE) {
> > + data->bytes_xfered = min(len, mmc->max_req_size);
> > + if (transfer == SDCARD_CTRL_DATA_TRANSFER_READ && !direct) {
> > + sg_copy_from_buffer(data->sg, sg_nents(data->sg),
> > + host->buffer, data->bytes_xfered);
> > + }
> > + }
> > +
> > + mmc_request_done(mmc, mrq);
> > +}
> > +
> > +static void
> > +litex_set_clk(struct litex_mmc_host *host, unsigned int clk_freq)
> > +{
> > + u32 div = clk_freq ? host->freq / clk_freq : 256;
> > +
> > + div = roundup_pow_of_two(div);
> > + div = min_t(u32, max_t(u32, div, 2), 256);
>
> No need for the _t-variants if you make the constants unsigned (e.g. 2U).

Done.

> > + dev_info(&host->dev->dev, "sdclk_freq=%d: set to %d via div=%d\n",
> > + clk_freq, host->freq / div, div);
> > + litex_write16(host->sdphy + LITEX_PHY_CLOCKERDIV, div);
> > +}
>
> > +static int
> > +litex_mmc_probe(struct platform_device *pdev)
> > +{
> > + struct litex_mmc_host *host;
> > + struct mmc_host *mmc;
> > + struct device_node *cpu;
> > + int ret;
> > +
> > + mmc = mmc_alloc_host(sizeof(struct litex_mmc_host), &pdev->dev);
> > + /* 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;`
> > + */
> > + if (!mmc)
> > + return -ENOMEM;
> > +
> > + host = mmc_priv(mmc);
> > + host->mmc = mmc;
> > + host->dev = pdev;
> > +
> > + host->clock = 0;
> > + 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;
> > + }
> > +
> > + init_completion(&host->cmd_done);
> > + host->irq = platform_get_irq(pdev, 0);
>
> platform_get_irq_optional()
>
> So interrupts should not be required in the DT bindings.

Got it.

> > + if (host->irq < 0)
> > + dev_err(&pdev->dev, "Failed to get IRQ, using polling\n");
>
> This is not an error condition: dev_info() or dev_warn().

OK.

> > +
> > + /* 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;
> > +
> > + ret = dma_set_mask(&pdev->dev, DMA_BIT_MASK(32));
> > + if (ret)
> > + goto err_free_host;
> > +
> > + host->buf_size = mmc->max_req_size * 2;
> > + host->buffer = dma_alloc_coherent(&pdev->dev, host->buf_size,
> > + &host->dma, GFP_DMA);
> > + if (host->buffer == NULL) {
> > + ret = -ENOMEM;
> > + goto err_free_host;
> > + }
> > +
> > + host->sdphy = devm_platform_ioremap_resource_byname(pdev, "phy");
>
> So reg-names is required ;-)

Fixed in the DT bindings document.

> > + if (IS_ERR(host->sdphy)) {
> > + ret = PTR_ERR(host->sdphy);
> > + goto err_free_dma;
> > + }
> > +
> > + host->sdcore = devm_platform_ioremap_resource_byname(pdev, "core");
> > + if (IS_ERR(host->sdcore)) {
> > + ret = PTR_ERR(host->sdcore);
> > + goto err_free_dma;
> > + }
> > +
> > + host->sdreader = devm_platform_ioremap_resource_byname(pdev, "reader");
> > + if (IS_ERR(host->sdreader)) {
> > + ret = PTR_ERR(host->sdreader);
> > + goto err_free_dma;
> > + }
> > +
> > + host->sdwriter = devm_platform_ioremap_resource_byname(pdev, "writer");
> > + if (IS_ERR(host->sdwriter)) {
> > + ret = PTR_ERR(host->sdwriter);
> > + goto err_free_dma;
> > + }
> > +
> > + if (host->irq > 0) {
> > + host->sdirq = devm_platform_ioremap_resource_byname(pdev, "irq");
>
> So you need a "minItems: 4" for reg{,-names} in the DT bindings.

Ditto.

> > + if (IS_ERR(host->sdirq)) {
> > + ret = PTR_ERR(host->sdirq);
> > + goto err_free_dma;
> > + }
> > + }
> > +
> > + mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
> > + mmc->ops = &litex_mmc_ops;
> > +
> > + mmc->f_min = 12.5e6;
> > + mmc->f_max = 50e6;
> > +
> > + ret = mmc_of_parse(mmc);
> > + if (ret)
> > + goto err_free_dma;
> > +
> > + /* 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_FULL_PWR_CYCLE |
> > + MMC_CAP2_NO_SDIO;
> > +
> > + platform_set_drvdata(pdev, host);
> > +
> > + ret = mmc_add_host(mmc);
> > + if (ret < 0)
> > + goto err_free_dma;
> > +
> > + /* ensure DMA bus masters are disabled */
> > + litex_write8(host->sdreader + LITEX_BLK2MEM_ENA, 0);
> > + litex_write8(host->sdwriter + LITEX_MEM2BLK_ENA, 0);
> > +
> > + /* set up interrupt handler */
> > + if (host->irq > 0) {
> > + ret = request_irq(host->irq, litex_mmc_interrupt, 0,
> > + "litex-mmc", mmc);
> > + if (ret < 0) {
> > + dev_err(&pdev->dev,
> > + "irq setup error %d, using polling\n", ret);
> > + host->irq = 0;
> > + }
> > + }
> > +
> > + /* enable card-change interrupts, or else ask for polling */
> > + if (host->irq > 0) {
> > + litex_write32(host->sdirq + LITEX_IRQ_PENDING,
> > + SDIRQ_CARD_DETECT); /* clears it */
> > + litex_write32(host->sdirq + LITEX_IRQ_ENABLE,
> > + SDIRQ_CARD_DETECT);
> > + } else {
> > + mmc->caps |= MMC_CAP_NEEDS_POLL;
> > + }
> > +
> > + return 0;
> > +
> > +err_free_dma:
> > + dma_free_coherent(&pdev->dev, host->buf_size, host->buffer, host->dma);
> > +err_free_host:
> > + mmc_free_host(mmc);
> > + return ret;
> > +}
>

Thanks again,
--Gabriel