| Message ID | 20240215180102.13887-1-fancer.lancer@gmail.com |
|---|---|
| Headers | show |
| Series | spi: dw: Auto-detect number of native CS | expand |
On Thu, Feb 15, 2024 at 09:00:47PM +0300, Serge Semin wrote: > Aside with the FIFO depth and DFS field size it's possible to auto-detect > a number of native chip-select synthesized in the DW APB/AHB SSI IP-core. > It can be done just by writing ones to the SER register. The number of > writable flags in the register is limited by the SSI_NUM_SLAVES IP-core > synthesize parameter. All the upper flags are read-only and wired to zero. > Based on that let's add the number of native CS auto-detection procedure > so the low-level platform drivers wouldn't need to manually set it up > unless it's required to set a constraint due to platform-specific reasons > (for instance, due to a hardware bug). ... > + /* > + * Try to detect the number of native chip-selects if the platform > + * driver didn't set it up. There can be up to 16 lines configured. > + */ > + if (!dws->num_cs) { > + u32 ser; > + > + dw_writel(dws, DW_SPI_SER, 0xffff); GENMASK() ? > + ser = dw_readl(dws, DW_SPI_SER); > + dw_writel(dws, DW_SPI_SER, 0); Would it actually change the physical line state? If so, we may not do this. > + dws->num_cs = hweight16(ser); Why 16 and not u16 & dw_writew()/readw()? > + } I'm wondering why this can't be the default num_cs = ...autodetected... device_property_read(..., &num_cs);
The main goal of the short series is to provide a procedure implementing the auto-detection of the number of native Chip-Select signals supported by the controller. The suggested algorithm is straightforward. It relies on the fact that the SER register writable flags reflects the actual number of available native chip-select signals. So the DW APB/AHB SSI driver now tests the SER register for having the writable bits, calculates the number of CS signals based on the number of set flags and then initializes the num_cs private data field based on that, which then will be passed to the SPI-core subsystem indicating the number of supported hardware chip-selects. The implemented procedure will be useful for the DW SSI device nodes not having the explicitly set "num-cs" property. In case if the property is specified it will be utilized instead of the auto-detection procedure. Besides of that a small cleanup patch is introduced in the head of the series. It converts the driver to using the BITS_TO_BYTES() macro instead of the hard-coded DIV_ROUND_UP()-based calculation of the number of bytes-per-transfer-word. Signed-off-by: Serge Semin <fancer.lancer@gmail.com> Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Andy Shevchenko <andy@kernel.org> Cc: linux-spi@vger.kernel.org Cc: linux-kernel@vger.kernel.org Serge Semin (3): spi: dw: Convert to using BITS_TO_BYTES() macro spi: dw: Add a number of native CS auto-detection spi: dw: Drop default number of CS setting drivers/spi/spi-dw-core.c | 20 ++++++++++++++++---- drivers/spi/spi-dw-mmio.c | 7 ++----- 2 files changed, 18 insertions(+), 9 deletions(-)