linux-kernel - Re: Re: [PATCH] spi: spi-amd: Add AMD SPI controller driver support

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Message-ID: <95455440-393d-f8aa-c213-dd746f184744@amd.com>
Date:   Tue, 14 Apr 2020 17:07:03 +0530
From:   Sanjay R Mehta <sanmehta@....com>
To:     Mark Brown <broonie@...nel.org>,
        Sanjay R Mehta <sanju.mehta@....com>
Cc:     Nehal-bakulchandra.Shah@....com, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] spi: spi-amd: Add AMD SPI controller driver support



On 4/14/2020 4:46 PM, Mark Brown wrote:
> On Sun, Apr 12, 2020 at 02:28:31PM -0500, Sanjay R Mehta wrote:
> 
>> +++ b/drivers/spi/spi-amd.c
>> @@ -0,0 +1,341 @@
>> +// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
>> +/*
>> + * AMD SPI controller driver
>> + *
> 
> Please make the entire comment a C++ one so things look more
> intentional.
> 
>> +#define DRIVER_NAME		"amd_spi"
> 
> This is unused.
> 
>> +/* M_CMD OP codes for SPI */
>> +#define SPI_XFER_TX		1
>> +#define SPI_XFER_RX		2
> 
> These constants should be namespaced, they're likely to collide with
> generic additions.
> 
>> +static void amd_spi_execute_opcode(struct spi_master *master)
>> +{
>> +	struct amd_spi *amd_spi = spi_master_get_devdata(master);
>> +	bool spi_busy;
>> +
>> +	/* Set ExecuteOpCode bit in the CTRL0 register */
>> +	amd_spi_setclear_reg32(master, AMD_SPI_CTRL0_REG, AMD_SPI_EXEC_CMD,
>> +			       AMD_SPI_EXEC_CMD);
>> +
>> +	/* poll for SPI bus to become idle */
>> +	spi_busy = (ioread32((u8 __iomem *)amd_spi->io_remap_addr +
>> +		    AMD_SPI_CTRL0_REG) & AMD_SPI_BUSY) == AMD_SPI_BUSY;
>> +	while (spi_busy) {
>> +		set_current_state(TASK_INTERRUPTIBLE);
>> +		schedule();
>> +		set_current_state(TASK_RUNNING);
>> +		spi_busy = (ioread32((u8 __iomem *)amd_spi->io_remap_addr +
>> +			    AMD_SPI_CTRL0_REG) & AMD_SPI_BUSY) == AMD_SPI_BUSY;
>> +	}
> 
> This is a weird way to busy wait - usually you'd use a cpu_relax()
> rather than a schedule().  There's also no timeout here so we could busy
> wait for ever if something goes wrong.
> 
>> +static int amd_spi_master_setup(struct spi_device *spi)
>> +{
>> +	struct spi_master *master = spi->master;
>> +	struct amd_spi *amd_spi = spi_master_get_devdata(master);
>> +
>> +	amd_spi->chip_select = spi->chip_select;
>> +	amd_spi_select_chip(master);
> 
> This looks like it will potentially affect devices other than the
> current one.  setup() may be called while other devices are active it
> shouldn't do that.
> 
>> +		} else if (m_cmd & SPI_XFER_RX) {
>> +			/* Store no. of bytes to be received from
>> +			 * FIFO
>> +			 */
>> +			rx_len = xfer->len;
>> +			buffer = (u8 *)xfer->rx_buf;
> 
>> +		/* Read data from FIFO to receive buffer  */
>> +		for (i = 0; i < rx_len; i++)
>> +			buffer[i] = ioread8((u8 __iomem *)amd_spi->io_remap_addr
>> +					    + AMD_SPI_FIFO_BASE
>> +					    + tx_len + i);
> 
> This will only work for messages with a single receive transfer, if
> there are multiple transfers then you'll need to store multiple buffers
> and their lengths.
> 
>> +static int amd_spi_master_transfer(struct spi_master *master,
>> +				   struct spi_message *msg)
>> +{
>> +	struct amd_spi *amd_spi = spi_master_get_devdata(master);
>> +
>> +	/*
>> +	 * Extract spi_transfers from the spi message and
>> +	 * program the controller.
>> +	 */
>> +	amd_spi_fifo_xfer(amd_spi, msg);
>> +
>> +	return 0;
>> +}
> 
> This function is completely redundant, just inline amd_spi_fifo_xfer().
> It also ignores all errors which isn't great.
> 
>> +	/* Initialize the spi_master fields */
>> +	master->bus_num = 0;
>> +	master->num_chipselect = 4;
>> +	master->mode_bits = 0;
>> +	master->flags = 0;
> 
> This device is single duplex so should flag that.
> 
>> +	err = spi_register_master(master);
>> +	if (err) {
>> +		dev_err(dev, "error registering SPI controller\n");
>> +		goto err_iounmap;
> 
> It's best to print the error code to help people debug things.

Thanks Mark for the feedback. Will make all the suggested changes.
>