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Date: Mon, 3 Feb 2020 14:33:11 -0600
From: Eddie James <eajames@...ux.vnet.ibm.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>,
Eddie James <eajames@...ux.ibm.com>
Cc: linux-spi <linux-spi@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Mark Brown <broonie@...nel.org>, Joel Stanley <joel@....id.au>,
Andrew Jeffery <andrew@...id.au>
Subject: Re: [PATCH] spi: Add FSI-attached SPI controller driver
On 1/30/20 10:37 AM, Andy Shevchenko wrote:
> On Wed, Jan 29, 2020 at 10:09 PM Eddie James <eajames@...ux.ibm.com> wrote:
>> There exists a set of SPI controllers on some POWER processors that may
>> be accessed through the FSI bus. Add a driver to traverse the FSI CFAM
>> engine that can access and drive the SPI controllers. This driver would
>> typically be used by a baseboard management controller (BMC).
> ...
>
>> +#include <linux/bitfield.h>
>> +#include <linux/bits.h>
>> +#include <linux/of.h>
> ...
>
>> +struct fsi_spi {
>> + struct device *dev;
> Isn't fsl->dev the same?
> Perhaps kernel doc to explain the difference?
No, it's not the same, as dev here is the SPI controller. I'll add a
comment.
>
>> + struct fsi_device *fsi;
>> + u32 base;
>> +};
> ...
>
>> +static int fsi_spi_read_reg(struct fsi_spi *ctx, u32 offset, u64 *value)
>> +{
>> + int rc;
>> + __be32 cmd_be;
>> + __be32 data_be;
>> + *value = 0ULL;
> Usually the pattern is don't pollute output on error condition. Any
> reason why you zeroing output beforehand?
Well otherwise I have to store another 64 bit int and do another
assignment at the end. This is an internal function and all the users
below know what's happening.
>
>> + cmd_be = cpu_to_be32(offset + ctx->base);
>> + rc = fsi_device_write(ctx->fsi, FSI2SPI_CMD, &cmd_be, sizeof(cmd_be));
>> + if (rc)
>> + return rc;
>> + return 0;
>> +}
> ...
>
>> + data_be = cpu_to_be32((value >> 32) & 0xFFFFFFFF);
> Redundant & 0xff... part.
>
>> + data_be = cpu_to_be32(value & 0xFFFFFFFF);
> Ditto.
>
> You may use upper_32_bits() / lower_32_bits() instead.
OK, thanks.
>
> ...
>
>> +static int fsi_spi_data_in(u64 in, u8 *rx, int len)
>> +{
>> + int i;
>> + int num_bytes = len > 8 ? 8 : len;
> min(len, 8);
Sure.
>
>> + for (i = 0; i < num_bytes; ++i)
>> + rx[i] = (u8)((in >> (8 * ((num_bytes - 1) - i))) & 0xffULL);
> Redundant & 0xffULL part.
>
> Isn't it NIH of get_unalinged_be64 / le64 or something similar?
No, these are shift in/out operations. The read register will also have
previous operations data in them and must be extracted with only the
correct number of bytes.
>
>> + return num_bytes;
>> +}
>> +static int fsi_spi_data_out(u64 *out, const u8 *tx, int len)
>> +{
> Ditto as for above function. (put_unaligned ...)
>
>> +}
> ...
>
>> + dev_info(ctx->dev, "Resetting SPI controller.\n");
> info?! Why?
>
>> + rc = fsi_spi_write_reg(ctx, SPI_FSI_CLOCK_CFG,
>> + SPI_FSI_CLOCK_CFG_RESET2);
>> + return rc;
> return fsi_spi_write_reg();
>
> ...
>
>> + return ((64 - seq->bit) / 8) - 2;
> Too many parentheses.
I prefer using 2 extra characters to make it much clearer at a glance.
>
> ...
>
>> +static int fsi_spi_sequence_transfer(struct fsi_spi *ctx,
>> + struct fsi_spi_sequence *seq,
>> + struct spi_transfer *transfer)
>> +{
>> + int loops = 1;
>> + int idx = 0;
>> + int rc;
>> + u8 len;
>> + u8 rem = 0;
>> + if (transfer->len > 8) {
>> + loops = transfer->len / 8;
>> + rem = transfer->len - (loops * 8);
>> + len = 8;
>> + } else {
>> + len = transfer->len;
>> + }
> len = min(transfer->len, 8);
>
> loops = transfer->len / len;
> rem = transfer->len % len;
Sure.
>
> (I think compiler is clever enough to find out that the division can be avoided)
>
> ...and drop assignments in definition block.
>
> I didn't look carefully in the implementation, but I believe there is
> still room for improvement / optimization.
>
>> + if (loops > 1) {
>> + rc = fsi_spi_write_reg(ctx, SPI_FSI_COUNTER_CFG,
>> + SPI_FSI_COUNTER_CFG_LOOPS(loops - 1));
>> + if (rc) {
>> + /* Ensure error returns < 0 in this case. */
> I didn't get why this case is special? Why not to be consistent with
> return value?
Sure, will fix, this was leftover from some testing.
>
>> + if (rc > 0)
>> + rc = -rc;
>> +
>> + return rc;
>> + }
>> + return loops;
> If we return here the amount of loops...
>
>> + }
>> +
>> + return 0;
> ...why here is 0?
>
> I think more consistency is required.
Will refactor.
>
>> +}
> ...
>
>> +static int fsi_spi_transfer_data(struct fsi_spi *ctx,
>> + struct spi_transfer *transfer)
>> +{
> Can you refactor to tx and rx parts?
Why?
>
>> + return 0;
>> +}
> ...
>
>> + do {
>> + rc = fsi_spi_read_reg(ctx, SPI_FSI_STATUS, &status);
>> + if (rc)
>> + return rc;
>> +
>> + if (status & (SPI_FSI_STATUS_ANY_ERROR |
>> + SPI_FSI_STATUS_TDR_FULL |
>> + SPI_FSI_STATUS_RDR_FULL)) {
>> + rc = fsi_spi_reset(ctx);
>> + if (rc)
>> + return rc;
>> +
>> + continue;
> I forgot if this to be infinite loop or if it's going to check
> previous seq_state value. In any case this code is a bit fishy. Needs
> comments / refactoring.
I'll add a timeout.
>
>> + }
>> +
>> + seq_state = status & SPI_FSI_STATUS_SEQ_STATE;
>> + } while (seq_state && (seq_state != SPI_FSI_STATUS_SEQ_STATE_IDLE));
> ...
>
>> + if ((clock_cfg & (SPI_FSI_CLOCK_CFG_MM_ENABLE |
>> + SPI_FSI_CLOCK_CFG_ECC_DISABLE |
>> + SPI_FSI_CLOCK_CFG_MODE |
>> + SPI_FSI_CLOCK_CFG_SCK_RECV_DEL |
>> + SPI_FSI_CLOCK_CFG_SCK_DIV)) != wanted_clock_cfg)
>> + rc = fsi_spi_write_reg(ctx, SPI_FSI_CLOCK_CFG,
>> + wanted_clock_cfg);
> Missed {} ?
No? It's one line under the if.
>
>> +
>> + return rc;
>> +}
> ...
>
>> + rc = fsi_slave_read(fsi->slave, 0x2860, &root_ctrl_8,
> What is this magic for?
Added comment.
>
>> + sizeof(root_ctrl_8));
>> + if (rc)
>> + return rc;
> ...
>
>> +static int fsi_spi_remove(struct device *dev)
>> +{
>> + return 0;
>> +}
> Why do you need this?
Will drop it.
Thanks for the review!
Eddie
>
> ...
>
>> +static struct fsi_driver fsi_spi_driver = {
>> + .id_table = fsi_spi_ids,
>> + .drv = {
>> + .name = "spi-fsi",
>> + .bus = &fsi_bus_type,
> Why is it not in the module_fsi_driver() macro?
>
>> + .probe = fsi_spi_probe,
>> + .remove = fsi_spi_remove,
>> + },
>> +};
>> +
>> +module_fsi_driver(fsi_spi_driver);
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