On 7/18/23 15:18, Marek Szyprowski wrote:
Samsung DSIM used in older Exynos SoCs (like Exynos 4210, 4x12, 3250) doesn't report empty level of packer header FIFO. In case of those SoCs, use the old way of waiting for empty command tranfsfer FIFO, removed recently by commit 14806c641582 ("Drain command transfer FIFO before transfer"). Fixes: 14806c641582 ("Drain command transfer FIFO before transfer") Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> --- If I remember right, the problem with waiting for the empty command transfer FIFO was there from the begging of the Exynos DSI driver and Tomash Figa and Andrzej Hajda used a workaround based on waiting until the DSIM_SFR_HEADER_FULL bit gets cleared. So far it worked well enough on the older Exynos SoCs, but indeed there is no point using it on the properly working hardware, like Exynos 5433 or IMX. Marek Szyprowski --- drivers/gpu/drm/bridge/samsung-dsim.c | 11 +++++++++-- include/drm/bridge/samsung-dsim.h | 1 + 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c index 9b7a00bafeaa..80eb268d5868 100644 --- a/drivers/gpu/drm/bridge/samsung-dsim.c +++ b/drivers/gpu/drm/bridge/samsung-dsim.c @@ -412,6 +412,7 @@ static const struct samsung_dsim_driver_data exynos3_dsi_driver_data = { .m_min = 41, .m_max = 125, .min_freq = 500, + .has_broken_fifoctrl_emptyhdr = 1, };static const struct samsung_dsim_driver_data exynos4_dsi_driver_data = {@@ -428,6 +429,7 @@ static const struct samsung_dsim_driver_data exynos4_dsi_driver_data = { .m_min = 41, .m_max = 125, .min_freq = 500, + .has_broken_fifoctrl_emptyhdr = 1, };static const struct samsung_dsim_driver_data exynos5_dsi_driver_data = {@@ -1009,8 +1011,13 @@ static int samsung_dsim_wait_for_hdr_fifo(struct samsung_dsim *dsi) do { u32 reg = samsung_dsim_read(dsi, DSIM_FIFOCTRL_REG);- if (reg & DSIM_SFR_HEADER_EMPTY)- return 0; + if (!dsi->driver_data->has_broken_fifoctrl_emptyhdr) { + if (reg & DSIM_SFR_HEADER_EMPTY) + return 0; + } else { + if (!(reg & DSIM_SFR_HEADER_FULL)) + return 0;
Would it make sense to at least wait a little bit on the old hardware , so the data can actually leave the FIFO and be put on the line ?
I mean, imagine you have e.g. a byte of the FIFO space available (i.e. FIFO is not full), and you attempt to put in two bytes. The FIFO would overflow. If you wait a bit, then there is a chance this overflow condition is avoided.
